If a misfit task is affined to a subset of the possible CPUs, we need to
verify that one of these CPUs can fit it. Otherwise the load balancer
code will continuously trigger needlessly leading the balance_interval
to increase in return and eventually end up with a situation where real
imbalances take a long time to address because of this impossible
imbalance situation.
This can happen in Android world where it's common for background tasks
to be restricted to little cores.
Similarly if we can't fit the biggest core, triggering misfit is
pointless as it is the best we can ever get on this system.
To be able to detect that; we use asym_cap_list to iterate through
capacities in the system to see if the task is able to run at a higher
capacity level based on its p->cpus_ptr. We do that when the affinity
change, a fair task is forked, or when a task switched to fair policy.
We store the max_allowed_capacity in task_struct to allow for cheap
comparison in the fast path.
Improve check_misfit_status() function by removing redundant checks.
misfit_task_load will be 0 if the task can't move to a bigger CPU. And
nohz_balancer_kick() already checks for cpu_check_capacity() before
calling check_misfit_status().
Test:
=====
Add
trace_printk("balance_interval = %lu\n", interval)
in get_sd_balance_interval().
run
if [ "$MASK" != "0" ]; then
adb shell "taskset -a $MASK cat /dev/zero > /dev/null"
fi
sleep 10
// parse ftrace buffer counting the occurrence of each valaue
Where MASK is either:
* 0: no busy task running
* 1: busy task is pinned to 1 cpu; handled today to not cause
misfit
* f: busy task pinned to little cores, simulates busy background
task, demonstrates the problem to be fixed
Results:
========
Note how occurrence of balance_interval = 128 overshoots for MASK = f.
BEFORE
------
MASK=0
1 balance_interval = 175
120 balance_interval = 128
846 balance_interval = 64
55 balance_interval = 63
215 balance_interval = 32
2 balance_interval = 31
2 balance_interval = 16
4 balance_interval = 8
1870 balance_interval = 4
65 balance_interval = 2
MASK=1
27 balance_interval = 175
37 balance_interval = 127
840 balance_interval = 64
167 balance_interval = 63
449 balance_interval = 32
84 balance_interval = 31
304 balance_interval = 16
1156 balance_interval = 8
2781 balance_interval = 4
428 balance_interval = 2
MASK=f
1 balance_interval = 175
1328 balance_interval = 128
44 balance_interval = 64
101 balance_interval = 63
25 balance_interval = 32
5 balance_interval = 31
23 balance_interval = 16
23 balance_interval = 8
4306 balance_interval = 4
177 balance_interval = 2
AFTER
-----
Note how the high values almost disappear for all MASK values. The
system has background tasks that could trigger the problem without
simulate it even with MASK=0.
MASK=0
103 balance_interval = 63
19 balance_interval = 31
194 balance_interval = 8
4827 balance_interval = 4
179 balance_interval = 2
MASK=1
131 balance_interval = 63
1 balance_interval = 31
87 balance_interval = 8
3600 balance_interval = 4
7 balance_interval = 2
MASK=f
8 balance_interval = 127
182 balance_interval = 63
3 balance_interval = 31
9 balance_interval = 16
415 balance_interval = 8
3415 balance_interval = 4
21 balance_interval = 2
Signed-off-by: Qais Yousef <qyousef@layalina.io>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240324004552.999936-3-qyousef@layalina.io
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Merge tag 'v6.9-rc1' into sched/core, to pick up fixes and to refresh the branch
Signed-off-by: Ingo Molnar <mingo@kernel.org>
from hotplugged memory rather than only from main memory. Series
"implement "memmap on memory" feature on s390".
- More folio conversions from Matthew Wilcox in the series
"Convert memcontrol charge moving to use folios"
"mm: convert mm counter to take a folio"
- Chengming Zhou has optimized zswap's rbtree locking, providing
significant reductions in system time and modest but measurable
reductions in overall runtimes. The series is "mm/zswap: optimize the
scalability of zswap rb-tree".
- Chengming Zhou has also provided the series "mm/zswap: optimize zswap
lru list" which provides measurable runtime benefits in some
swap-intensive situations.
- And Chengming Zhou further optimizes zswap in the series "mm/zswap:
optimize for dynamic zswap_pools". Measured improvements are modest.
- zswap cleanups and simplifications from Yosry Ahmed in the series "mm:
zswap: simplify zswap_swapoff()".
- In the series "Add DAX ABI for memmap_on_memory", Vishal Verma has
contributed several DAX cleanups as well as adding a sysfs tunable to
control the memmap_on_memory setting when the dax device is hotplugged
as system memory.
- Johannes Weiner has added the large series "mm: zswap: cleanups",
which does that.
- More DAMON work from SeongJae Park in the series
"mm/damon: make DAMON debugfs interface deprecation unignorable"
"selftests/damon: add more tests for core functionalities and corner cases"
"Docs/mm/damon: misc readability improvements"
"mm/damon: let DAMOS feeds and tame/auto-tune itself"
- In the series "mm/mempolicy: weighted interleave mempolicy and sysfs
extension" Rakie Kim has developed a new mempolicy interleaving policy
wherein we allocate memory across nodes in a weighted fashion rather
than uniformly. This is beneficial in heterogeneous memory environments
appearing with CXL.
- Christophe Leroy has contributed some cleanup and consolidation work
against the ARM pagetable dumping code in the series "mm: ptdump:
Refactor CONFIG_DEBUG_WX and check_wx_pages debugfs attribute".
- Luis Chamberlain has added some additional xarray selftesting in the
series "test_xarray: advanced API multi-index tests".
- Muhammad Usama Anjum has reworked the selftest code to make its
human-readable output conform to the TAP ("Test Anything Protocol")
format. Amongst other things, this opens up the use of third-party
tools to parse and process out selftesting results.
- Ryan Roberts has added fork()-time PTE batching of THP ptes in the
series "mm/memory: optimize fork() with PTE-mapped THP". Mainly
targeted at arm64, this significantly speeds up fork() when the process
has a large number of pte-mapped folios.
- David Hildenbrand also gets in on the THP pte batching game in his
series "mm/memory: optimize unmap/zap with PTE-mapped THP". It
implements batching during munmap() and other pte teardown situations.
The microbenchmark improvements are nice.
- And in the series "Transparent Contiguous PTEs for User Mappings" Ryan
Roberts further utilizes arm's pte's contiguous bit ("contpte
mappings"). Kernel build times on arm64 improved nicely. Ryan's series
"Address some contpte nits" provides some followup work.
- In the series "mm/hugetlb: Restore the reservation" Breno Leitao has
fixed an obscure hugetlb race which was causing unnecessary page faults.
He has also added a reproducer under the selftest code.
- In the series "selftests/mm: Output cleanups for the compaction test",
Mark Brown did what the title claims.
- Kinsey Ho has added the series "mm/mglru: code cleanup and refactoring".
- Even more zswap material from Nhat Pham. The series "fix and extend
zswap kselftests" does as claimed.
- In the series "Introduce cpu_dcache_is_aliasing() to fix DAX
regression" Mathieu Desnoyers has cleaned up and fixed rather a mess in
our handling of DAX on archiecctures which have virtually aliasing data
caches. The arm architecture is the main beneficiary.
- Lokesh Gidra's series "per-vma locks in userfaultfd" provides dramatic
improvements in worst-case mmap_lock hold times during certain
userfaultfd operations.
- Some page_owner enhancements and maintenance work from Oscar Salvador
in his series
"page_owner: print stacks and their outstanding allocations"
"page_owner: Fixup and cleanup"
- Uladzislau Rezki has contributed some vmalloc scalability improvements
in his series "Mitigate a vmap lock contention". It realizes a 12x
improvement for a certain microbenchmark.
- Some kexec/crash cleanup work from Baoquan He in the series "Split
crash out from kexec and clean up related config items".
- Some zsmalloc maintenance work from Chengming Zhou in the series
"mm/zsmalloc: fix and optimize objects/page migration"
"mm/zsmalloc: some cleanup for get/set_zspage_mapping()"
- Zi Yan has taught the MM to perform compaction on folios larger than
order=0. This a step along the path to implementaton of the merging of
large anonymous folios. The series is named "Enable >0 order folio
memory compaction".
- Christoph Hellwig has done quite a lot of cleanup work in the
pagecache writeback code in his series "convert write_cache_pages() to
an iterator".
- Some modest hugetlb cleanups and speedups in Vishal Moola's series
"Handle hugetlb faults under the VMA lock".
- Zi Yan has changed the page splitting code so we can split huge pages
into sizes other than order-0 to better utilize large folios. The
series is named "Split a folio to any lower order folios".
- David Hildenbrand has contributed the series "mm: remove
total_mapcount()", a cleanup.
- Matthew Wilcox has sought to improve the performance of bulk memory
freeing in his series "Rearrange batched folio freeing".
- Gang Li's series "hugetlb: parallelize hugetlb page init on boot"
provides large improvements in bootup times on large machines which are
configured to use large numbers of hugetlb pages.
- Matthew Wilcox's series "PageFlags cleanups" does that.
- Qi Zheng's series "minor fixes and supplement for ptdesc" does that
also. S390 is affected.
- Cleanups to our pagemap utility functions from Peter Xu in his series
"mm/treewide: Replace pXd_large() with pXd_leaf()".
- Nico Pache has fixed a few things with our hugepage selftests in his
series "selftests/mm: Improve Hugepage Test Handling in MM Selftests".
- Also, of course, many singleton patches to many things. Please see
the individual changelogs for details.
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Merge tag 'mm-stable-2024-03-13-20-04' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull MM updates from Andrew Morton:
- Sumanth Korikkar has taught s390 to allocate hotplug-time page frames
from hotplugged memory rather than only from main memory. Series
"implement "memmap on memory" feature on s390".
- More folio conversions from Matthew Wilcox in the series
"Convert memcontrol charge moving to use folios"
"mm: convert mm counter to take a folio"
- Chengming Zhou has optimized zswap's rbtree locking, providing
significant reductions in system time and modest but measurable
reductions in overall runtimes. The series is "mm/zswap: optimize the
scalability of zswap rb-tree".
- Chengming Zhou has also provided the series "mm/zswap: optimize zswap
lru list" which provides measurable runtime benefits in some
swap-intensive situations.
- And Chengming Zhou further optimizes zswap in the series "mm/zswap:
optimize for dynamic zswap_pools". Measured improvements are modest.
- zswap cleanups and simplifications from Yosry Ahmed in the series
"mm: zswap: simplify zswap_swapoff()".
- In the series "Add DAX ABI for memmap_on_memory", Vishal Verma has
contributed several DAX cleanups as well as adding a sysfs tunable to
control the memmap_on_memory setting when the dax device is
hotplugged as system memory.
- Johannes Weiner has added the large series "mm: zswap: cleanups",
which does that.
- More DAMON work from SeongJae Park in the series
"mm/damon: make DAMON debugfs interface deprecation unignorable"
"selftests/damon: add more tests for core functionalities and corner cases"
"Docs/mm/damon: misc readability improvements"
"mm/damon: let DAMOS feeds and tame/auto-tune itself"
- In the series "mm/mempolicy: weighted interleave mempolicy and sysfs
extension" Rakie Kim has developed a new mempolicy interleaving
policy wherein we allocate memory across nodes in a weighted fashion
rather than uniformly. This is beneficial in heterogeneous memory
environments appearing with CXL.
- Christophe Leroy has contributed some cleanup and consolidation work
against the ARM pagetable dumping code in the series "mm: ptdump:
Refactor CONFIG_DEBUG_WX and check_wx_pages debugfs attribute".
- Luis Chamberlain has added some additional xarray selftesting in the
series "test_xarray: advanced API multi-index tests".
- Muhammad Usama Anjum has reworked the selftest code to make its
human-readable output conform to the TAP ("Test Anything Protocol")
format. Amongst other things, this opens up the use of third-party
tools to parse and process out selftesting results.
- Ryan Roberts has added fork()-time PTE batching of THP ptes in the
series "mm/memory: optimize fork() with PTE-mapped THP". Mainly
targeted at arm64, this significantly speeds up fork() when the
process has a large number of pte-mapped folios.
- David Hildenbrand also gets in on the THP pte batching game in his
series "mm/memory: optimize unmap/zap with PTE-mapped THP". It
implements batching during munmap() and other pte teardown
situations. The microbenchmark improvements are nice.
- And in the series "Transparent Contiguous PTEs for User Mappings"
Ryan Roberts further utilizes arm's pte's contiguous bit ("contpte
mappings"). Kernel build times on arm64 improved nicely. Ryan's
series "Address some contpte nits" provides some followup work.
- In the series "mm/hugetlb: Restore the reservation" Breno Leitao has
fixed an obscure hugetlb race which was causing unnecessary page
faults. He has also added a reproducer under the selftest code.
- In the series "selftests/mm: Output cleanups for the compaction
test", Mark Brown did what the title claims.
- Kinsey Ho has added the series "mm/mglru: code cleanup and
refactoring".
- Even more zswap material from Nhat Pham. The series "fix and extend
zswap kselftests" does as claimed.
- In the series "Introduce cpu_dcache_is_aliasing() to fix DAX
regression" Mathieu Desnoyers has cleaned up and fixed rather a mess
in our handling of DAX on archiecctures which have virtually aliasing
data caches. The arm architecture is the main beneficiary.
- Lokesh Gidra's series "per-vma locks in userfaultfd" provides
dramatic improvements in worst-case mmap_lock hold times during
certain userfaultfd operations.
- Some page_owner enhancements and maintenance work from Oscar Salvador
in his series
"page_owner: print stacks and their outstanding allocations"
"page_owner: Fixup and cleanup"
- Uladzislau Rezki has contributed some vmalloc scalability
improvements in his series "Mitigate a vmap lock contention". It
realizes a 12x improvement for a certain microbenchmark.
- Some kexec/crash cleanup work from Baoquan He in the series "Split
crash out from kexec and clean up related config items".
- Some zsmalloc maintenance work from Chengming Zhou in the series
"mm/zsmalloc: fix and optimize objects/page migration"
"mm/zsmalloc: some cleanup for get/set_zspage_mapping()"
- Zi Yan has taught the MM to perform compaction on folios larger than
order=0. This a step along the path to implementaton of the merging
of large anonymous folios. The series is named "Enable >0 order folio
memory compaction".
- Christoph Hellwig has done quite a lot of cleanup work in the
pagecache writeback code in his series "convert write_cache_pages()
to an iterator".
- Some modest hugetlb cleanups and speedups in Vishal Moola's series
"Handle hugetlb faults under the VMA lock".
- Zi Yan has changed the page splitting code so we can split huge pages
into sizes other than order-0 to better utilize large folios. The
series is named "Split a folio to any lower order folios".
- David Hildenbrand has contributed the series "mm: remove
total_mapcount()", a cleanup.
- Matthew Wilcox has sought to improve the performance of bulk memory
freeing in his series "Rearrange batched folio freeing".
- Gang Li's series "hugetlb: parallelize hugetlb page init on boot"
provides large improvements in bootup times on large machines which
are configured to use large numbers of hugetlb pages.
- Matthew Wilcox's series "PageFlags cleanups" does that.
- Qi Zheng's series "minor fixes and supplement for ptdesc" does that
also. S390 is affected.
- Cleanups to our pagemap utility functions from Peter Xu in his series
"mm/treewide: Replace pXd_large() with pXd_leaf()".
- Nico Pache has fixed a few things with our hugepage selftests in his
series "selftests/mm: Improve Hugepage Test Handling in MM
Selftests".
- Also, of course, many singleton patches to many things. Please see
the individual changelogs for details.
* tag 'mm-stable-2024-03-13-20-04' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (435 commits)
mm/zswap: remove the memcpy if acomp is not sleepable
crypto: introduce: acomp_is_async to expose if comp drivers might sleep
memtest: use {READ,WRITE}_ONCE in memory scanning
mm: prohibit the last subpage from reusing the entire large folio
mm: recover pud_leaf() definitions in nopmd case
selftests/mm: skip the hugetlb-madvise tests on unmet hugepage requirements
selftests/mm: skip uffd hugetlb tests with insufficient hugepages
selftests/mm: dont fail testsuite due to a lack of hugepages
mm/huge_memory: skip invalid debugfs new_order input for folio split
mm/huge_memory: check new folio order when split a folio
mm, vmscan: retry kswapd's priority loop with cache_trim_mode off on failure
mm: add an explicit smp_wmb() to UFFDIO_CONTINUE
mm: fix list corruption in put_pages_list
mm: remove folio from deferred split list before uncharging it
filemap: avoid unnecessary major faults in filemap_fault()
mm,page_owner: drop unnecessary check
mm,page_owner: check for null stack_record before bumping its refcount
mm: swap: fix race between free_swap_and_cache() and swapoff()
mm/treewide: align up pXd_leaf() retval across archs
mm/treewide: drop pXd_large()
...
The 'idle_balance()' function hasn't existed for years, and there's no
load_balance_newidle() either - both are sched_balance_newidle() today.
Reported-by: Honglei Wang <jameshongleiwang@126.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/ZfAwNufbiyt/5biu@gmail.com
Standardize scheduler load-balancing function names on the
sched_balance_() prefix.
Also use 'dst' instead of 'idlest', because it's not really
true that we return the 'idlest' group or CPU, we sort by
idle-exit latency and only return the idlest CPUs from the
lowest-latency set of CPUs.
The true 'idlest' CPUs often remain idle for a long time
and are never returned as long as the system is under-loaded.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-14-mingo@kernel.org
Standardize scheduler load-balancing function names on the
sched_balance_() prefix.
Also use 'dst' instead of 'idlest', because it's not really
true that we return the 'idlest' group or CPU, we sort by
idle-exit latency and only return the idlest CPUs from the
lowest-latency set of CPUs.
The true 'idlest' CPUs often remain idle for a long time
and are never returned as long as the system is under-loaded.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-13-mingo@kernel.org
Standardize scheduler load-balancing function names on the
sched_balance_() prefix.
Also use 'dst' instead of 'idlest': while historically correct,
today it's not really true anymore that we return the 'idlest'
group or CPU, we sort by idle-exit latency and only return the
idlest CPUs from the lowest-latency set of CPUs.
The true 'idlest' CPUs often remain idle for a long time
and are never returned as long as the system is under-loaded.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-12-mingo@kernel.org
Make two naming changes:
1)
Standardize scheduler load-balancing function names on the
sched_balance_() prefix.
2)
Similar to find_busiest_queue(), the find_busiest_group() naming
has become a bit of a misnomer: the 'busiest' qualifier to this
function was historically correct but in the current code
in quite a few cases we will not pick the 'busiest' group - but the best
(possible) group we can balance from based on a complex set of
constraints.
So name it a bit more neutrally, similar to the 'src/dst' nomenclature
we are already using when moving tasks between runqueues, and also
use the sched_balance_ prefix: sched_balance_find_src_group().
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-9-mingo@kernel.org
The find_busiest_queue() naming has two small quirks:
- Scheduler functions that deal with runqueues usually have a rq_ prefix
or _rq postfix, but this function has neither.
- Plus the 'busiest' qualifier to this function was historically
correct, but has become somewhat of a misnomer: in quite a few
cases we will not pick the busiest runqueue - but the best
(possible) runqueue we can balance tasks from. So name it a
bit more neutrally, similar to the 'src/dst' nomenclature
we are already using when moving tasks between runqueues.
To fix both quirks, and to standardize scheduler load-balancing
function names on the sched_balance_() prefix, rename the
function to sched_balance_find_src_rq().
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-7-mingo@kernel.org
Standardize scheduler load-balancing function names on the
sched_balance_() prefix.
Also load_balance() has become somewhat of a misnomer: historically
it was the first and primary load-balancing function that was called,
but with the introduction of sched domains, it's become a lower
layer function that balances runqueues.
Rename it to sched_balance_rq() accordingly.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-6-mingo@kernel.org
run_rebalance_domains() is a misnomer, as it doesn't only
run rebalance_domains(), but since the introduction of the
NOHZ code it also runs nohz_idle_balance().
Rename it to sched_balance_softirq(), reflecting its more
generic purpose and that it's a softirq handler.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308111819.1101550-2-mingo@kernel.org
The first sentence of the comment explaining run_rebalance_domains()
is historic and not true anymore:
* run_rebalance_domains is triggered when needed from the scheduler tick.
... contradicted/modified by the second sentence:
* Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).
Avoid that kind of confusion straight away and explain from what
places sched_balance_softirq() is triggered.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20240308105901.1096078-9-mingo@kernel.org
Fix two typos:
- There's no such thing as 'nohz_balancing_kick', the
flag is named 'BALANCE' and is capitalized: NOHZ_BALANCE_KICK.
- Likewise there's no such thing as a 'pending nohz_balance_kick'
either, the NOHZ_BALANCE_KICK flag is all upper-case.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240308105901.1096078-8-mingo@kernel.org
So the scheduler has two such comment blocks, with '=' used as a double underline:
/*
* VRUNTIME
* ========
*
'========' also happens to be a Git conflict marker, throwing off a simple
search in an editor for this pattern.
Change them to '-------' type of underline instead - it looks just as good.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240308105901.1096078-7-mingo@kernel.org
The cpu_idle_type enum has the confusingly inverted property
that 'not idle' is 1, and 'idle' is '0'.
This resulted in a number of unnecessary complications in the code.
Reverse the order, remove the CPU_NOT_IDLE type, and convert
all code to a natural boolean form.
It's much more readable:
- enum cpu_idle_type idle = this_rq->idle_balance ?
- CPU_IDLE : CPU_NOT_IDLE;
-
+ enum cpu_idle_type idle = this_rq->idle_balance;
--------------------------------
- if (env->idle == CPU_NOT_IDLE || !busiest->sum_nr_running)
+ if (!env->idle || !busiest->sum_nr_running)
--------------------------------
And gets rid of the double negation in these usages:
- if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
+ if (env->idle && env->src_rq->nr_running <= 1)
Furthermore, this makes code much more obvious where there's
differentiation between CPU_IDLE and CPU_NEWLY_IDLE.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Gautham R. Shenoy" <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20240308105901.1096078-4-mingo@kernel.org
The 'balancing' spinlock added in:
08c183f31b ("[PATCH] sched: add option to serialize load balancing")
... is taken when the SD_SERIALIZE flag is set in a domain, but in reality it
is a glorified global atomic flag serializing the load-balancing of
those domains.
It doesn't have any explicit locking semantics per se: we just
spin_trylock() it.
Turn it into a ... global atomic flag. This makes it more
clear what is going on here, and reduces overhead and code
size a bit:
# kernel/sched/fair.o: [x86-64 defconfig]
text data bss dec hex filename
60730 2721 104 63555 f843 fair.o.before
60718 2721 104 63543 f837 fair.o.after
Also document the flag a bit.
No change in functionality intended.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://lore.kernel.org/r/20240308105901.1096078-2-mingo@kernel.org
Memoryless nodes do not have any memory to migrate to, so, as an
optimization, stop trying it.
Link: https://lkml.kernel.org/r/20240219041920.1183-1-byungchul@sk.com
Link: https://lkml.kernel.org/r/20240216111502.79759-1-byungchul@sk.com
Fixes: c574bbe917 ("NUMA balancing: optimize page placement for memory tiering system")
Signed-off-by: Byungchul Park <byungchul@sk.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Benjamin Segall <bsegall@google.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
SD_SHARE_PKG_RESOURCES is a bit of a misnomer: its naming suggests that
it's sharing all 'package resources' - while in reality it's specifically
for sharing the LLC only.
Rename it to SD_SHARE_LLC to reduce confusion.
[ mingo: Rewrote the confusing changelog as well. ]
Suggested-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Link: https://lore.kernel.org/r/20240210113924.1130448-5-alexs@kernel.org
sched_use_asym_prio() checks whether CPU priorities should be used. It
makes sense to check for the SD_ASYM_PACKING() inside the function.
Since both sched_asym() and sched_group_asym() use sched_use_asym_prio(),
remove the now superfluous checks for the flag in various places.
Signed-off-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240210113924.1130448-4-alexs@kernel.org
sched_use_asym_prio() and sched_asym_prefer() are used together in various
places. Consolidate them into a single function sched_asym().
The existing sched_asym() function is only used when collecting statistics
of a scheduling group. Rename it as sched_group_asym(), and remove the
obsolete function description.
This makes the code easier to read. No functional changes.
Signed-off-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240210113924.1130448-3-alexs@kernel.org
The 'sds' argument is not used in the sched_asym() function anymore, remove it.
Fixes: c9ca07886a ("sched/fair: Do not even the number of busy CPUs via asym_packing")
Signed-off-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240210113924.1130448-2-alexs@kernel.org
When comparing the current struct sched_group with the yet-busiest
domain in update_sd_pick_busiest(), if the two groups have the same
group type, we're currently doing a bit of unnecessary work for any
group >= group_misfit_task. We're comparing the two groups, and then
returning only if false (the group in question is not the busiest).
Otherwise, we break out, do an extra unnecessary conditional check that's
vacuously false for any group type > group_fully_busy, and then always
return true.
Let's just return directly in the switch statement instead. This doesn't
change the size of vmlinux with llvm 17 (not surprising given that all
of this is inlined in load_balance()), but it does shrink load_balance()
by 88 bytes on x86. Given that it also improves readability, this seems
worth doing.
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20240206043921.850302-4-void@manifault.com
In update_sd_pick_busiest(), when comparing two sched groups that are
both of type group_misfit_task, we currently consider the new group as
busier than the current busiest group even if the new group has the
same misfit task load as the current busiest group. We can avoid some
unnecessary writes if we instead only consider the newest group to be
the busiest if it has a higher load than the current busiest. This
matches the behavior of other group types where we compare load, such as
two groups that are both overloaded.
Let's update the group_misfit_task type comparison to also only update
the busiest group in the event of strict inequality.
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20240206043921.850302-3-void@manifault.com
In update_sd_lb_stats(), when we're iterating over the sched groups that
comprise a sched domain, we're skipping the call to
update_sd_pick_busiest() for the sched group that contains the local /
destination CPU. We use a goto to skip the call, but we could just as
easily check !local_group, as there's no other logic that we need to
skip with the goto. Let's remove the goto, and check for !local_group in
the if statement instead.
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20240206043921.850302-2-void@manifault.com
When picking a CPU on task wakeup, select_idle_core() has to take
into account the scheduling domain where the function looks for the CPU.
This is because the "isolcpus" kernel command line option can remove CPUs
from the domain to isolate them from other SMT siblings.
This change replaces the set of CPUs allowed to run the task from
p->cpus_ptr by the intersection of p->cpus_ptr and sched_domain_span(sd)
which is stored in the 'cpus' argument provided by select_idle_cpu().
Fixes: 9fe1f127b9 ("sched/fair: Merge select_idle_core/cpu()")
Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240110131707.437301-2-keisuke.nishimura@inria.fr
When picking a CPU on task wakeup, select_idle_smt() has to take
into account the scheduling domain of @target. This is because the
"isolcpus" kernel command line option can remove CPUs from the domain to
isolate them from other SMT siblings.
This fix checks if the candidate CPU is in the target scheduling domain.
Commit:
df3cb4ea1f ("sched/fair: Fix wrong cpu selecting from isolated domain")
... originally introduced this fix by adding the check of the scheduling
domain in the loop.
However, commit:
3e6efe87cd ("sched/fair: Remove redundant check in select_idle_smt()")
... accidentally removed the check. Bring it back.
Fixes: 3e6efe87cd ("sched/fair: Remove redundant check in select_idle_smt()")
Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240110131707.437301-1-keisuke.nishimura@inria.fr
Use existing helper function cpu_util_irq() instead of open-coding
access to ->avg_irq.
During review it was noted that ->avg_irq could be updated by a
different CPU than the one which is trying to access it.
->avg_irq is updated with WRITE_ONCE(), use READ_ONCE to access it
in order to avoid any compiler optimizations.
Signed-off-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240101154624.100981-3-sshegde@linux.vnet.ibm.com
There are helper functions called cpu_util_dl() and cpu_util_rt() which give
the average utilization of DL and RT respectively. But there are a few
places in code where access to these variables is open-coded.
Instead use the helper function so that code becomes simpler and easier to
maintain later on.
No functional changes intended.
Signed-off-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240101154624.100981-2-sshegde@linux.vnet.ibm.com
There's a few cases of nested #ifdefs in the scheduler code
that can be simplified:
#ifdef DEFINE_A
...code block...
#ifdef DEFINE_A <-- This is a duplicate.
...code block...
#endif
#else
#ifndef DEFINE_A <-- This is also duplicate.
...code block...
#endif
#endif
More details about the script and methods used to find these code
patterns can be found at:
https://lore.kernel.org/all/20240118080326.13137-1-sshegde@linux.ibm.com/
No change in functionality intended.
[ mingo: Clarified the changelog. ]
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240216061433.535522-1-sshegde@linux.ibm.com
many places. The notable patch series are:
- nilfs2 folio conversion from Matthew Wilcox in "nilfs2: Folio
conversions for file paths".
- Additional nilfs2 folio conversion from Ryusuke Konishi in "nilfs2:
Folio conversions for directory paths".
- IA64 remnant removal in Heiko Carstens's "Remove unused code after
IA-64 removal".
- Arnd Bergmann has enabled the -Wmissing-prototypes warning everywhere
in "Treewide: enable -Wmissing-prototypes". This had some followup
fixes:
- Nathan Chancellor has cleaned up the hexagon build in the series
"hexagon: Fix up instances of -Wmissing-prototypes".
- Nathan also addressed some s390 warnings in "s390: A couple of
fixes for -Wmissing-prototypes".
- Arnd Bergmann addresses the same warnings for MIPS in his series
"mips: address -Wmissing-prototypes warnings".
- Baoquan He has made kexec_file operate in a top-down-fitting manner
similar to kexec_load in the series "kexec_file: Load kernel at top of
system RAM if required"
- Baoquan He has also added the self-explanatory "kexec_file: print out
debugging message if required".
- Some checkstack maintenance work from Tiezhu Yang in the series
"Modify some code about checkstack".
- Douglas Anderson has disentangled the watchdog code's logging when
multiple reports are occurring simultaneously. The series is "watchdog:
Better handling of concurrent lockups".
- Yuntao Wang has contributed some maintenance work on the crash code in
"crash: Some cleanups and fixes".
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Merge tag 'mm-nonmm-stable-2024-01-09-10-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull non-MM updates from Andrew Morton:
"Quite a lot of kexec work this time around. Many singleton patches in
many places. The notable patch series are:
- nilfs2 folio conversion from Matthew Wilcox in 'nilfs2: Folio
conversions for file paths'.
- Additional nilfs2 folio conversion from Ryusuke Konishi in 'nilfs2:
Folio conversions for directory paths'.
- IA64 remnant removal in Heiko Carstens's 'Remove unused code after
IA-64 removal'.
- Arnd Bergmann has enabled the -Wmissing-prototypes warning
everywhere in 'Treewide: enable -Wmissing-prototypes'. This had
some followup fixes:
- Nathan Chancellor has cleaned up the hexagon build in the series
'hexagon: Fix up instances of -Wmissing-prototypes'.
- Nathan also addressed some s390 warnings in 's390: A couple of
fixes for -Wmissing-prototypes'.
- Arnd Bergmann addresses the same warnings for MIPS in his series
'mips: address -Wmissing-prototypes warnings'.
- Baoquan He has made kexec_file operate in a top-down-fitting manner
similar to kexec_load in the series 'kexec_file: Load kernel at top
of system RAM if required'
- Baoquan He has also added the self-explanatory 'kexec_file: print
out debugging message if required'.
- Some checkstack maintenance work from Tiezhu Yang in the series
'Modify some code about checkstack'.
- Douglas Anderson has disentangled the watchdog code's logging when
multiple reports are occurring simultaneously. The series is
'watchdog: Better handling of concurrent lockups'.
- Yuntao Wang has contributed some maintenance work on the crash code
in 'crash: Some cleanups and fixes'"
* tag 'mm-nonmm-stable-2024-01-09-10-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (157 commits)
crash_core: fix and simplify the logic of crash_exclude_mem_range()
x86/crash: use SZ_1M macro instead of hardcoded value
x86/crash: remove the unused image parameter from prepare_elf_headers()
kdump: remove redundant DEFAULT_CRASH_KERNEL_LOW_SIZE
scripts/decode_stacktrace.sh: strip unexpected CR from lines
watchdog: if panicking and we dumped everything, don't re-enable dumping
watchdog/hardlockup: use printk_cpu_sync_get_irqsave() to serialize reporting
watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting
watchdog/hardlockup: adopt softlockup logic avoiding double-dumps
kexec_core: fix the assignment to kimage->control_page
x86/kexec: fix incorrect end address passed to kernel_ident_mapping_init()
lib/trace_readwrite.c:: replace asm-generic/io with linux/io
nilfs2: cpfile: fix some kernel-doc warnings
stacktrace: fix kernel-doc typo
scripts/checkstack.pl: fix no space expression between sp and offset
x86/kexec: fix incorrect argument passed to kexec_dprintk()
x86/kexec: use pr_err() instead of kexec_dprintk() when an error occurs
nilfs2: add missing set_freezable() for freezable kthread
kernel: relay: remove relay_file_splice_read dead code, doesn't work
docs: submit-checklist: remove all of "make namespacecheck"
...
When a CPU is taken offline, the contribution of its cfs_rqs to task_groups'
load may remain and will negatively impact the calculation of the share of
the online CPUs.
To fix this bug, clear the contribution of an offlining CPU to task groups'
load and skip its contribution while it is inactive.
Here's the reproducer of the anomaly, by Imran Khan:
"So far I have encountered only one rather lengthy way of reproducing this issue,
which is as follows:
1. Take a KVM guest (booted with 4 CPUs and can be scaled up to 124 CPUs) and
create 2 custom cgroups: /sys/fs/cgroup/cpu/test_group_1 and /sys/fs/cgroup/
cpu/test_group_2
2. Assign a CPU intensive workload to each of these cgroups and start the
workload.
For my tests I am using following app:
int main(int argc, char *argv[])
{
unsigned long count, i, val;
if (argc != 2) {
printf("usage: ./a.out <number of random nums to generate> \n");
return 0;
}
count = strtoul(argv[1], NULL, 10);
printf("Generating %lu random numbers \n", count);
for (i = 0; i < count; i++) {
val = rand();
val = val % 2;
//usleep(1);
}
printf("Generated %lu random numbers \n", count);
return 0;
}
Also since the system is booted with 4 CPUs, in order to completely load the
system I am also launching 4 instances of same test app under:
/sys/fs/cgroup/cpu/
3. We can see that both of the cgroups get similar CPU time:
# systemd-cgtop --depth 1
Path Tasks %CPU Memory Input/s Output/s
/ 659 - 5.5G - -
/system.slice - - 5.7G - -
/test_group_1 4 - - - -
/test_group_2 3 - - - -
/user.slice 31 - 56.5M - -
Path Tasks %CPU Memory Input/s Output/s
/ 659 394.6 5.5G - -
/test_group_2 3 65.7 - - -
/user.slice 29 55.1 48.0M - -
/test_group_1 4 47.3 - - -
/system.slice - 2.2 5.7G - -
Path Tasks %CPU Memory Input/s Output/s
/ 659 394.8 5.5G - -
/test_group_1 4 62.9 - - -
/user.slice 28 44.9 54.2M - -
/test_group_2 3 44.7 - - -
/system.slice - 0.9 5.7G - -
Path Tasks %CPU Memory Input/s Output/s
/ 659 394.4 5.5G - -
/test_group_2 3 58.8 - - -
/test_group_1 4 51.9 - - -
/user.slice 30 39.3 59.6M - -
/system.slice - 1.9 5.7G - -
Path Tasks %CPU Memory Input/s Output/s
/ 659 394.7 5.5G - -
/test_group_1 4 60.9 - - -
/test_group_2 3 57.9 - - -
/user.slice 28 43.5 36.9M - -
/system.slice - 3.0 5.7G - -
Path Tasks %CPU Memory Input/s Output/s
/ 659 395.0 5.5G - -
/test_group_1 4 66.8 - - -
/test_group_2 3 56.3 - - -
/user.slice 29 43.1 51.8M - -
/system.slice - 0.7 5.7G - -
4. Now move systemd-udevd to one of these test groups, say test_group_1, and
perform scale up to 124 CPUs followed by scale down back to 4 CPUs from the
host side.
5. Run the same workload i.e 4 instances of CPU hogger under /sys/fs/cgroup/cpu
and one instance of CPU hogger each in /sys/fs/cgroup/cpu/test_group_1 and
/sys/fs/cgroup/test_group_2.
It can be seen that test_group_1 (the one where systemd-udevd was moved) is getting
much less CPU time than the test_group_2, even though at this point of time both of
these groups have only CPU hogger running:
# systemd-cgtop --depth 1
Path Tasks %CPU Memory Input/s Output/s
/ 1219 - 5.4G - -
/system.slice - - 5.6G - -
/test_group_1 4 - - - -
/test_group_2 3 - - - -
/user.slice 26 - 91.3M - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 394.3 5.4G - -
/test_group_2 3 82.7 - - -
/test_group_1 4 14.3 - - -
/system.slice - 0.8 5.6G - -
/user.slice 26 0.4 91.2M - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 394.6 5.4G - -
/test_group_2 3 67.4 - - -
/system.slice - 24.6 5.6G - -
/test_group_1 4 12.5 - - -
/user.slice 26 0.4 91.2M - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 395.2 5.4G - -
/test_group_2 3 60.9 - - -
/system.slice - 27.9 5.6G - -
/test_group_1 4 12.2 - - -
/user.slice 26 0.4 91.2M - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 395.2 5.4G - -
/test_group_2 3 69.4 - - -
/test_group_1 4 13.9 - - -
/user.slice 28 1.6 92.0M - -
/system.slice - 1.0 5.6G - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 395.6 5.4G - -
/test_group_2 3 59.3 - - -
/test_group_1 4 14.1 - - -
/user.slice 28 1.3 92.2M - -
/system.slice - 0.7 5.6G - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 395.5 5.4G - -
/test_group_2 3 67.2 - - -
/test_group_1 4 11.5 - - -
/user.slice 28 1.3 92.5M - -
/system.slice - 0.6 5.6G - -
Path Tasks %CPU Memory Input/s Output/s
/ 1221 395.1 5.4G - -
/test_group_2 3 76.8 - - -
/test_group_1 4 12.9 - - -
/user.slice 28 1.3 92.8M - -
/system.slice - 1.2 5.6G - -
From sched_debug data it can be seen that in bad case the load.weight of per-CPU
sched entities corresponding to test_group_1 has reduced significantly and
also load_avg of test_group_1 remains much higher than that of test_group_2,
even though systemd-udevd stopped running long time back and at this point of
time both cgroups just have the CPU hogger app as running entity."
[ mingo: Added details from the original discussion, plus minor edits to the patch. ]
Reported-by: Imran Khan <imran.f.khan@oracle.com>
Tested-by: Imran Khan <imran.f.khan@oracle.com>
Tested-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Imran Khan <imran.f.khan@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Link: https://lore.kernel.org/r/20231223111545.62135-1-vincent.guittot@linaro.org
Running N CPU-bound tasks on an N CPUs platform:
- with asymmetric CPU capacity
- not being a DynamIq system (i.e. having a PKG level sched domain
without the SD_SHARE_PKG_RESOURCES flag set)
.. might result in a task placement where two tasks run on a big CPU
and none on a little CPU. This placement could be more optimal by
using all CPUs.
Testing platform:
Juno-r2:
- 2 big CPUs (1-2), maximum capacity of 1024
- 4 little CPUs (0,3-5), maximum capacity of 383
Testing workload ([1]):
Spawn 6 CPU-bound tasks. During the first 100ms (step 1), each tasks
is affine to a CPU, except for:
- one little CPU which is left idle.
- one big CPU which has 2 tasks affine.
After the 100ms (step 2), remove the cpumask affinity.
Behavior before the patch:
During step 2, the load balancer running from the idle CPU tags sched
domains as:
- little CPUs: 'group_has_spare'. Cf. group_has_capacity() and
group_is_overloaded(), 3 CPU-bound tasks run on a 4 CPUs
sched-domain, and the idle CPU provides enough spare capacity
regarding the imbalance_pct
- big CPUs: 'group_overloaded'. Indeed, 3 tasks run on a 2 CPUs
sched-domain, so the following path is used:
group_is_overloaded()
\-if (sgs->sum_nr_running <= sgs->group_weight) return true;
The following path which would change the migration type to
'migrate_task' is not taken:
calculate_imbalance()
\-if (env->idle != CPU_NOT_IDLE && env->imbalance == 0)
as the local group has some spare capacity, so the imbalance
is not 0.
The migration type requested is 'migrate_util' and the busiest
runqueue is the big CPU's runqueue having 2 tasks (each having a
utilization of 512). The idle little CPU cannot pull one of these
task as its capacity is too small for the task. The following path
is used:
detach_tasks()
\-case migrate_util:
\-if (util > env->imbalance) goto next;
After the patch:
As the number of failed balancing attempts grows (with
'nr_balance_failed'), progressively make it easier to migrate
a big task to the idling little CPU. A similar mechanism is
used for the 'migrate_load' migration type.
Improvement:
Running the testing workload [1] with the step 2 representing
a ~10s load for a big CPU:
Before patch: ~19.3s
After patch: ~18s (-6.7%)
Similar issue reported at:
https://lore.kernel.org/lkml/20230716014125.139577-1-qyousef@layalina.io/
Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Qais Yousef <qyousef@layalina.io>
Link: https://lore.kernel.org/r/20231206090043.634697-1-pierre.gondois@arm.com
With UTIL_EST_FASTUP now being permanent, we can take advantage of the
fact that the ewma jumps directly to a higher utilization at dequeue to
simplify util_est and remove the enqueued field.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Hongyan Xia <hongyan.xia2@arm.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20231201161652.1241695-3-vincent.guittot@linaro.org
sched_feat(UTIL_EST_FASTUP) has been added to easily disable the feature
in order to check for possibly related regressions. After 3 years, it has
never been used and no regression has been reported. Let's remove it
and make fast increase a permanent behavior.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Hongyan Xia <hongyan.xia2@arm.com>
Reviewed-by: Tang Yizhou <yizhou.tang@shopee.com>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn> [for the Chinese translation]
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20231201161652.1241695-2-vincent.guittot@linaro.org
These four functions have a normal definition for CONFIG_FAIR_GROUP_SCHED,
and empty one that is only referenced when FAIR_GROUP_SCHED is disabled
but CGROUP_SCHED is still enabled. If both are turned off, the functions
are still defined but the misisng prototype causes a W=1 warning:
kernel/sched/fair.c:12544:6: error: no previous prototype for 'free_fair_sched_group'
kernel/sched/fair.c:12546:5: error: no previous prototype for 'alloc_fair_sched_group'
kernel/sched/fair.c:12553:6: error: no previous prototype for 'online_fair_sched_group'
kernel/sched/fair.c:12555:6: error: no previous prototype for 'unregister_fair_sched_group'
Move the alternatives into the header as static inline functions with the
correct combination of #ifdef checks to avoid the warning without adding
even more complexity.
[A different patch with the same description got applied by accident
and was later reverted, but the original patch is still missing]
Link: https://lkml.kernel.org/r/20231123110506.707903-4-arnd@kernel.org
Fixes: 7aa55f2a59 ("sched/fair: Move unused stub functions to header")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Rich Felker <dalias@libc.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Tudor Ambarus <tudor.ambarus@linaro.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Since reweight_entity() may have chance to change the weight of
cfs_rq->curr entity, we should also update_min_vruntime() if
this is the case
Fixes: eab03c23c2 ("sched/eevdf: Fix vruntime adjustment on reweight")
Signed-off-by: Yiwei Lin <s921975628@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Abel Wu <wuyun.abel@bytedance.com>
Link: https://lore.kernel.org/r/20231117080106.12890-1-s921975628@gmail.com
The current method to take into account uclamp hints when estimating the
target frequency can end in a situation where the selected target
frequency is finally higher than uclamp hints, whereas there are no real
needs. Such cases mainly happen because we are currently mixing the
traditional scheduler utilization signal with the uclamp performance
hints. By adding these 2 metrics, we loose an important information when
it comes to select the target frequency, and we have to make some
assumptions which can't fit all cases.
Rework the interface between the scheduler and schedutil governor in order
to propagate all information down to the cpufreq governor.
effective_cpu_util() interface changes and now returns the actual
utilization of the CPU with 2 optional inputs:
- The minimum performance for this CPU; typically the capacity to handle
the deadline task and the interrupt pressure. But also uclamp_min
request when available.
- The maximum targeting performance for this CPU which reflects the
maximum level that we would like to not exceed. By default it will be
the CPU capacity but can be reduced because of some performance hints
set with uclamp. The value can be lower than actual utilization and/or
min performance level.
A new sugov_effective_cpu_perf() interface is also available to compute
the final performance level that is targeted for the CPU, after applying
some cpufreq headroom and taking into account all inputs.
With these 2 functions, schedutil is now able to decide when it must go
above uclamp hints. It now also has a generic way to get the min
performance level.
The dependency between energy model and cpufreq governor and its headroom
policy doesn't exist anymore.
eenv_pd_max_util() asks schedutil for the targeted performance after
applying the impact of the waking task.
[ mingo: Refined the changelog & C comments. ]
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20231122133904.446032-2-vincent.guittot@linaro.org
Lukasz Luba reported that a thread's util_est can significantly decrease as
a result of sharing the CPU with other threads.
The use case can be easily reproduced with a periodic task TA that runs 1ms
and sleeps 100us. When the task is alone on the CPU, its max utilization and
its util_est is around 888. If another similar task starts to run on the
same CPU, TA will have to share the CPU runtime and its maximum utilization
will decrease around half the CPU capacity (512) then TA's util_est will
follow this new maximum trend which is only the result of sharing the CPU
with others tasks.
Such situation can be detected with runnable_avg wich is close or
equal to util_avg when TA is alone, but increases above util_avg when TA
shares the CPU with other threads and wait on the runqueue.
[ We prefer an util_est that overestimate rather than under estimate
because in 1st case we will not provide enough performance to the
task which will remain under-provisioned, whereas in the other case we
will create some idle time which will enable to reduce contention and
as a result reduces the util_est so the overestimate will be transient
whereas the underestimate will remain. ]
[ mingo: Refined the changelog, added comments from the LKML discussion. ]
Reported-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/lkml/CAKfTPtDd-HhF-YiNTtL9i5k0PfJbF819Yxu4YquzfXgwi7voyw@mail.gmail.com/#t
Link: https://lore.kernel.org/r/20231122140119.472110-1-vincent.guittot@linaro.org
Cc: Hongyan Xia <hongyan.xia2@arm.com>
Low priority tasks (e.g., SCHED_OTHER) can suffer starvation if tasks
with higher priority (e.g., SCHED_FIFO) monopolize CPU(s).
RT Throttling has been introduced a while ago as a (mostly debug)
countermeasure one can utilize to reserve some CPU time for low priority
tasks (usually background type of work, e.g. workqueues, timers, etc.).
It however has its own problems (see documentation) and the undesired
effect of unconditionally throttling FIFO tasks even when no lower
priority activity needs to run (there are mechanisms to fix this issue
as well, but, again, with their own problems).
Introduce deadline servers to service low priority tasks needs under
starvation conditions. Deadline servers are built extending SCHED_DEADLINE
implementation to allow 2-level scheduling (a sched_deadline entity
becomes a container for lower priority scheduling entities).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/4968601859d920335cf85822eb573a5f179f04b8.1699095159.git.bristot@kernel.org
Now that trace_sched_stat_runtime() no longer takes a vruntime
argument, the task specific bits are identical between
update_curr_common() and update_curr().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tracing the runtime delta makes sense, observer can sum over time.
Tracing the absolute vruntime makes less sense, inconsistent:
absolute-vs-delta, but also vruntime delta can be computed from
runtime delta.
Removing the vruntime thing also makes the two tracepoint sites
identical, allowing to unify the code in a later patch.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
