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SubjectRe: [PATCH mm-unstable] lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default
On Wed, Jan 25, 2023 at 06:02:04PM -0800, Roman Gushchin wrote:
> On Sat, Jan 21, 2023 at 12:39:42PM +0900, Hyeonggon Yoo wrote:
> > 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%*
> >
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
>
> Nice!
>
> I checkout my very simple kmem performance test (1M allocations 8-bytes allocations)
> and it shows ~30% difference: 112319 us with vs 80836 us without.

Hello Roman,

Oh, it has higher impact on micro benchmark.

>
> Probably not that big for real workloads, but still nice to have.
>
> Acked-by: Roman Gushchin <roman.gushchin@linux.dev>

Thank you for kindly measuring impact of this patch
and giving ack!

> Thank you!
>

--
Thanks,
Hyeonggon

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