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SubjectRe: [PATCH mm-unstable] lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default
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.

Probably not that big for real workloads, but still nice to have.

Acked-by: Roman Gushchin <roman.gushchin@linux.dev>

Thank you!

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