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

[Davidlohr Bueso]

On Sat, 21 Jan 2023, 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@xxxxxxxxx>

Acked-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>