5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> 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@xxxxxxxxx Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Acked-by: Davidlohr Bueso <dave@xxxxxxxxxxxx> Cc: Ben Segall <bsegall@xxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Dennis Zhou <dennis@xxxxxxxxxx> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Muchun Song <muchun.song@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Valentin Schneider <vschneid@xxxxxxxxxx> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Luiz Capitulino <luizcap@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- lib/Kconfig.debug | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1136,13 +1136,16 @@ 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
