Petr Mladek f244b4dc53 printk: ringbuffer: Improve prb_next_seq() performance ... prb_next_seq() always iterates from the first known sequence number. In the worst case, it might loop 8k times for 256kB buffer, 15k times for 512kB buffer, and 64k times for 2MB buffer. It was reported that polling and reading using syslog interface might occupy 50% of CPU. Speedup the search by storing @id of the last finalized descriptor. The loop is still needed because the @id is stored and read in the best effort way. An atomic variable is used to keep the @id consistent. But the stores and reads are not serialized against each other. The descriptor could get reused in the meantime. The related sequence number will be used only when it is still valid. An invalid value should be read _only_ when there is a flood of messages and the ringbuffer is rapidly reused. The performance is the least problem in this case. Reported-by: Chunlei Wang <chunlei.wang@mediatek.com> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com> Reviewed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/1642770388-17327-1-git-send-email-quic_mojha@quicinc.com Link: https://lore.kernel.org/lkml/YXlddJxLh77DKfIO@alley/T/#m43062e8b2a17f8dbc8c6ccdb8851fb0dbaabbb14		2022-01-26 16:00:32 +01:00
..
bpf	bpf: Fix leakage under speculation on mispredicted branches	2021-06-14 23:06:10 +02:00
cgroup	sched: Change task_struct::state	2021-06-18 11:43:09 +02:00
configs	drivers/char: remove /dev/kmem for good	2021-05-07 00:26:34 -07:00
debug	printk changes for 5.14	2021-06-29 12:07:18 -07:00
dma	Merge branch 'stable/for-linus-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb	2021-06-23 09:04:07 -07:00
entry	tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed	2021-05-31 10:14:49 +02:00
events	Scheduler udpates for this cycle:	2021-06-28 12:14:19 -07:00
gcov	gcov: clang: drop support for clang-10 and older	2021-05-07 00:26:32 -07:00
irq	genirq: Export affinity setter for modules	2021-05-19 11:01:51 +02:00
kcsan	sched: Introduce task_is_running()	2021-06-18 11:43:07 +02:00
livepatch	Livepatching changes for 5.13	2021-04-27 18:14:38 -07:00
locking	Scheduler udpates for this cycle:	2021-06-28 12:14:19 -07:00
power	PM: sleep: fix typos in comments	2021-04-08 19:37:21 +02:00
printk	printk: ringbuffer: Improve prb_next_seq() performance	2022-01-26 16:00:32 +01:00
rcu	sched: Change task_struct::state	2021-06-18 11:43:09 +02:00
sched	Updates to the tick/nohz code in this cycle:	2021-06-28 12:22:06 -07:00
time	Updates to the tick/nohz code in this cycle:	2021-06-28 12:22:06 -07:00
trace	tracing: Do no increment trace_clock_global() by one	2021-06-18 09:10:00 -04:00
.gitignore	.gitignore: prefix local generated files with a slash	2021-05-02 00:43:35 +09:00
acct.c	kernel/acct.c: use #elif instead of #end and #elif	2020-12-15 22:46:15 -08:00
async.c	kernel/async.c: remove async_unregister_domain()	2021-05-07 00:26:33 -07:00
audit.c	lsm: separate security_task_getsecid() into subjective and objective variants	2021-03-22 15:23:32 -04:00
audit.h	audit: avoid -Wempty-body warning	2021-03-24 12:11:48 -04:00
audit_fsnotify.c	audit_alloc_mark(): don't open-code ERR_CAST()	2021-02-23 10:25:27 -05:00
audit_tree.c	fsnotify: generalize handle_inode_event()	2020-12-03 14:58:35 +01:00
audit_watch.c	fsnotify: generalize handle_inode_event()	2020-12-03 14:58:35 +01:00
auditfilter.c	lsm: separate security_task_getsecid() into subjective and objective variants	2021-03-22 15:23:32 -04:00
auditsc.c	audit/stable-5.13 PR 20210426	2021-04-27 13:50:58 -07:00
backtracetest.c
bounds.c
capability.c	capability: handle idmapped mounts	2021-01-24 14:27:16 +01:00
cfi.c	add support for Clang CFI	2021-04-08 16:04:20 -07:00
compat.c
configs.c
context_tracking.c
cpu.c	cpumask/hotplug: Fix cpu_dying() state tracking	2021-04-21 13:55:43 +02:00
cpu_pm.c
crash_core.c	crash_core, vmcoreinfo: append 'SECTION_SIZE_BITS' to vmcoreinfo	2021-06-16 09:24:42 -07:00
crash_dump.c
cred.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
delayacct.c	delayacct: Add sysctl to enable at runtime	2021-05-12 11:43:25 +02:00
dma.c
exec_domain.c
exit.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
extable.c
fail_function.c	fault-injection: handle EI_ETYPE_TRUE	2020-12-15 22:46:19 -08:00
fork.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
freezer.c	sched: Add get_current_state()	2021-06-18 11:43:08 +02:00
futex.c	Locking changes for this cycle:	2021-06-28 11:45:29 -07:00
gen_kheaders.sh	kbuild: redo fake deps at include/config/*.h	2021-04-25 05:26:10 +09:00
groups.c	groups: simplify struct group_info allocation	2021-02-26 09:41:03 -08:00
hung_task.c	sched: Change task_struct::state	2021-06-18 11:43:09 +02:00
iomem.c
irq_work.c	irq_work: Make irq_work_queue() NMI-safe again	2021-06-10 10:00:08 +02:00
jump_label.c	jump_label: Free jump_entry::key bit1 for build use	2021-05-12 14:54:55 +02:00
kallsyms.c	kallsyms: strip ThinLTO hashes from static functions	2021-04-08 16:04:21 -07:00
kcmp.c	Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2020-12-15 19:36:48 -08:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt	sched: Add CONFIG_SCHED_CORE help text	2021-06-01 16:00:10 +02:00
kcov.c
kexec.c
kexec_core.c	kexec: dump kmessage before machine_kexec	2021-05-07 00:26:32 -07:00
kexec_elf.c
kexec_file.c	kernel: kexec_file: fix error return code of kexec_calculate_store_digests()	2021-05-07 00:26:32 -07:00
kexec_internal.h	kexec: move machine_kexec_post_load() to public interface	2021-02-22 12:33:26 +00:00
kheaders.c
kmod.c	modules: add CONFIG_MODPROBE_PATH	2021-05-07 00:26:33 -07:00
kprobes.c	kprobes: Remove kprobe::fault_handler	2021-06-01 16:00:08 +02:00
ksysfs.c
kthread.c	Scheduler udpates for this cycle:	2021-06-28 12:14:19 -07:00
latencytop.c
Makefile	kbuild: update config_data.gz only when the content of .config is changed	2021-05-02 00:43:35 +09:00
module-internal.h
module.c	module: limit enabling module.sig_enforce	2021-06-22 11:13:19 -07:00
module_signature.c	module: harden ELF info handling	2021-01-19 10:24:45 +01:00
module_signing.c	module: harden ELF info handling	2021-01-19 10:24:45 +01:00
notifier.c
nsproxy.c	fixes-v5.11	2020-12-14 16:40:27 -08:00
padata.c
panic.c	panic: don't dump stack twice on warn	2020-11-14 11:26:04 -08:00
params.c	Modules updates for v5.11	2020-12-17 13:01:31 -08:00
pid.c	Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2020-12-15 19:36:48 -08:00
pid_namespace.c	fixes-v5.11	2020-12-14 16:40:27 -08:00
profile.c	kernel: Initialize cpumask before parsing	2021-04-10 13:35:54 +02:00
ptrace.c	sched: Change task_struct::state	2021-06-18 11:43:09 +02:00
range.c
reboot.c	reboot: Add hardware protection power-off	2021-06-21 13:08:36 +01:00
regset.c
relay.c	relay: allow the use of const callback structs	2020-12-15 22:46:18 -08:00
resource.c	kernel/resource: fix return code check in __request_free_mem_region	2021-05-14 19:41:32 -07:00
resource_kunit.c	resource: provide meaningful MODULE_LICENSE() in test suite	2020-11-25 18:52:35 +01:00
rseq.c	rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()	2021-04-14 18:04:09 +02:00
scftorture.c	scftorture: Add debug output for wrong-CPU warning	2021-01-04 13:53:41 -08:00
scs.c	scs: switch to vmapped shadow stacks	2020-12-01 10:30:28 +00:00
seccomp.c	seccomp: Support atomic "addfd + send reply"	2021-06-28 12:49:52 -07:00
signal.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
smp.c	smp: Fix smp_call_function_single_async prototype	2021-05-06 15:33:49 +02:00
smpboot.c	sched/core: Initialize the idle task with preemption disabled	2021-05-12 13:01:45 +02:00
smpboot.h
softirq.c	sched: Introduce task_is_running()	2021-06-18 11:43:07 +02:00
stackleak.c
stacktrace.c
static_call.c	static_call: Fix unused variable warn w/o MODULE	2021-04-09 13:22:12 +02:00
stop_machine.c	stop_machine: Add caller debug info to queue_stop_cpus_work	2021-03-23 16:01:58 +01:00
sys.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
sys_ni.c	Add Landlock, a new LSM from Mickaël Salaün <mic@linux.microsoft.com>	2021-05-01 18:50:44 -07:00
sysctl-test.c
sysctl.c	Merge branch 'sched/urgent' into sched/core, to pick up fixes	2021-06-03 19:00:49 +02:00
task_work.c	kasan: record task_work_add() call stack	2021-04-30 11:20:42 -07:00
taskstats.c	treewide: rename nla_strlcpy to nla_strscpy.	2020-11-16 08:08:54 -08:00
test_kprobes.c
torture.c	torture: Replace torture_init_begin string with %s	2021-03-08 14:22:28 -08:00
tracepoint.c	tracepoints: Code clean up	2021-02-09 12:27:29 -05:00
tsacct.c
ucount.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
uid16.c
uid16.h
umh.c	kernel/umh.c: fix some spelling mistakes	2021-05-07 00:26:34 -07:00
up.c	A set of locking related fixes and updates:	2021-05-09 13:07:03 -07:00
user-return-notifier.c
user.c	Reimplement RLIMIT_MEMLOCK on top of ucounts	2021-04-30 14:14:02 -05:00
user_namespace.c	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace	2021-06-28 20:39:26 -07:00
usermode_driver.c	bpf: Fix umd memory leak in copy_process()	2021-03-19 22:23:19 +01:00
utsname.c
utsname_sysctl.c
watch_queue.c	watch_queue: rectify kernel-doc for init_watch()	2021-01-26 11:16:34 +00:00
watchdog.c	watchdog: reliable handling of timestamps	2021-05-22 15:09:07 -10:00
watchdog_hld.c
workqueue.c	wq: handle VM suspension in stall detection	2021-05-20 12:58:30 -04:00
workqueue_internal.h