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Vincent Guittot b4c9c9f156 sched/fair: Prefer prev cpu in asymmetric wakeup path 
During fast wakeup path, scheduler always check whether local or prev
cpus are good candidates for the task before looking for other cpus in
the domain. With commit b7a331615d ("sched/fair: Add asymmetric CPU
capacity wakeup scan") the heterogenous system gains a dedicated path
but doesn't try to reuse prev cpu whenever possible. If the previous
cpu is idle and belong to the LLC domain, we should check it 1st
before looking for another cpu because it stays one of the best
candidate and this also stabilizes task placement on the system.

This change aligns asymmetric path behavior with symmetric one and reduces
cases where the task migrates across all cpus of the sd_asym_cpucapacity
domains at wakeup.

This change does not impact normal EAS mode but only the overloaded case or
when EAS is not used.

- On hikey960 with performance governor (EAS disable)

./perf bench sched pipe -T -l 50000
             mainline           w/ patch
# migrations   999364                  0
ops/sec        149313(+/-0.28%)   182587(+/- 0.40) +22%

- On hikey with performance governor

./perf bench sched pipe -T -l 50000
             mainline           w/ patch
# migrations        0                  0
ops/sec         47721(+/-0.76%)    47899(+/- 0.56) +0.4%

According to test on hikey, the patch doesn't impact symmetric system
compared to current implementation (only tested on arm64)

Also read the uclamped value of task's utilization at most twice instead
instead each time we compare task's utilization with cpu's capacity.

Fixes: b7a331615d ("sched/fair: Add asymmetric CPU capacity wakeup scan")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20201029161824.26389-1-vincent.guittot@linaro.org
2020-11-10 18:38:48 +01:00
arch A single commit harmonizing the x86 and ARM64 Hyper-V constants namespace. 2020-10-12 15:30:32 -07:00
block block5.9-2020-10-08 2020-10-08 18:48:34 -07:00
certs
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-08-30 15:53:44 -07:00
Documentation EFI changes for v5.10: 2020-10-12 13:26:49 -07:00
drivers This tree introduces static_call(), which is the idea of static_branch() 2020-10-12 13:58:15 -07:00
fs EFI changes for v5.10: 2020-10-12 13:26:49 -07:00
include Clean up the paravirt code after the removal of 32-bit Xen PV support. 2020-10-12 15:15:24 -07:00
init bootconfig: init: make xbc_namebuf static 2020-09-18 22:17:05 -04:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel sched/fair: Prefer prev cpu in asymmetric wakeup path 2020-11-10 18:38:48 +01:00
lib These are the locking updates for v5.10: 2020-10-12 13:06:20 -07:00
LICENSES
mm These are the locking updates for v5.10: 2020-10-12 13:06:20 -07:00
net openvswitch: handle DNAT tuple collision 2020-10-08 12:20:35 -07:00
samples treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
scripts Merge branch 'kcsan' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into locking/core 2020-10-09 08:56:02 +02:00
security EFI changes for v5.10: 2020-10-12 13:26:49 -07:00
sound sound fixes for 5.9-rc7 2020-09-24 09:00:05 -07:00
tools This tree introduces static_call(), which is the idea of static_branch() 2020-10-12 13:58:15 -07:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM: fix memory leak in kvm_io_bus_unregister_dev() 2020-09-11 13:15:11 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2020-09-01 12:53:42 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap MAINTAINERS: Antoine Tenart's email address 2020-10-11 10:31:10 -07:00
COPYING
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -06:00
Kbuild
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Scheduler changes for v5.10: 2020-10-12 12:56:01 -07:00
Makefile Linux 5.9 2020-10-11 14:15:50 -07:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.