| From: Hyeonggon Yoo <42.hyeyoo@gmail.com> |
| Subject: lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default |
| Date: Sat, 21 Jan 2023 12:39:42 +0900 |
| |
| 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> |
| --- |
| |
| |
| --- a/lib/Kconfig.debug~lib-kconfigdebug-do-not-enable-debug_preempt-by-default |
| +++ a/lib/Kconfig.debug |
| @@ -1246,13 +1246,16 @@ 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 |
| _ |
