On Thu, Jan 26, 2023 at 03:23:39PM -0800, Andrew Morton wrote: > > The patch titled > Subject: lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default > has been added to the -mm mm-nonmm-unstable branch. Its filename is > lib-kconfigdebug-do-not-enable-debug_preempt-by-default.patch > > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-kconfigdebug-do-not-enable-debug_preempt-by-default.patch > > This patch will later appear in the mm-nonmm-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > 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@xxxxxxxxx > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> > 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: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Thanks for picking this up! but looks like missing Mel's Acked-by. could you add that please? > 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> > --- > > lib/Kconfig.debug | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > --- a/lib/Kconfig.debug~lib-kconfigdebug-do-not-enable-debug_preempt-by-default > +++ a/lib/Kconfig.debug > @@ -1176,13 +1176,16 @@ 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 > _ > > Patches currently in -mm which might be from 42.hyeyoo@xxxxxxxxx are > > mm-page_owner-record-single-timestamp-value-for-high-order-allocations.patch > lib-kconfigdebug-do-not-enable-debug_preempt-by-default.patch >
