5.15-stable review patch. If anyone has any objections, please let me know.
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From: Hyeonggon Yoo 42.hyeyoo@gmail.com
commit cc6003916ed46d7a67d91ee32de0f9138047d55f upstream.
In workloads where this_cpu operations are frequently performed, enabling DEBUG_PREEMPT may result in significant increase in runtime overhead due to frequent invocation of __this_cpu_preempt_check() function.
This can be demonstrated through benchmarks such as hackbench where this configuration results in a 10% reduction in performance, primarily due to the added overhead within memcg charging path.
Therefore, do not to enable DEBUG_PREEMPT by default and make users aware of its potential impact on performance in some workloads.
hackbench-process-sockets debug_preempt no_debug_preempt Amean 1 0.4743 ( 0.00%) 0.4295 * 9.45%* Amean 4 1.4191 ( 0.00%) 1.2650 * 10.86%* Amean 7 2.2677 ( 0.00%) 2.0094 * 11.39%* Amean 12 3.6821 ( 0.00%) 3.2115 * 12.78%* Amean 21 6.6752 ( 0.00%) 5.7956 * 13.18%* Amean 30 9.6646 ( 0.00%) 8.5197 * 11.85%* Amean 48 15.3363 ( 0.00%) 13.5559 * 11.61%* Amean 79 24.8603 ( 0.00%) 22.0597 * 11.27%* Amean 96 30.1240 ( 0.00%) 26.8073 * 11.01%*
Link: https://lkml.kernel.org/r/20230121033942.350387-1-42.hyeyoo@gmail.com Signed-off-by: Hyeonggon Yoo 42.hyeyoo@gmail.com Acked-by: Roman Gushchin roman.gushchin@linux.dev Acked-by: Mel Gorman mgorman@techsingularity.net Acked-by: Davidlohr Bueso dave@stgolabs.net Cc: Ben Segall bsegall@google.com Cc: Christoph Lameter cl@linux.com Cc: Daniel Bristot de Oliveira bristot@redhat.com Cc: David Rientjes rientjes@google.com Cc: Dennis Zhou dennis@kernel.org Cc: Dietmar Eggemann dietmar.eggemann@arm.com Cc: Ingo Molnar mingo@redhat.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: Juri Lelli juri.lelli@redhat.com Cc: Matthew Wilcox willy@infradead.org Cc: Muchun Song muchun.song@linux.dev Cc: Pekka Enberg penberg@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Shakeel Butt shakeelb@google.com Cc: Steven Rostedt (Google) rostedt@goodmis.org Cc: Tejun Heo tj@kernel.org Cc: Valentin Schneider vschneid@redhat.com Cc: Vincent Guittot vincent.guittot@linaro.org Cc: Vlastimil Babka vbabka@suse.cz Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: Luiz Capitulino luizcap@amazon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- lib/Kconfig.debug | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1226,13 +1226,16 @@ config DEBUG_TIMEKEEPING config DEBUG_PREEMPT bool "Debug preemptible kernel" depends on DEBUG_KERNEL && PREEMPTION && TRACE_IRQFLAGS_SUPPORT - default y help If you say Y here then the kernel will use a debug variant of the commonly used smp_processor_id() function and will print warnings if kernel code uses it in a preemption-unsafe way. Also, the kernel will detect preemption count underflows.
+ This option has potential to introduce high runtime overhead, + depending on workload as it triggers debugging routines for each + this_cpu operation. It should only be used for debugging purposes. + menu "Lock Debugging (spinlocks, mutexes, etc...)"
config LOCK_DEBUGGING_SUPPORT