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SubjectRe: [Cocci] [PATCH 1/2] scripts: coccicheck: Change default value for parallelism


On Thu, 24 Sep 2020, Sumera Priyadarsini wrote:

> By default, coccicheck utilizes all available threads to implement
> parallelisation. However, when all available threads are used,
> a decrease in performance is noted. The elapsed time is minimum
> when at most one thread per core is used.
>
> For example, on benchmarking the semantic patch kfree.cocci for
> usb/serial using hyperfine, the outputs obtained for J=5 and J=2
> are 1.32 and 1.90 times faster than those for J=10 and J=9
> respectively for two separate runs. For the larger drivers/staging
> directory, minimium elapsed time is obtained for J=3 which is 1.86
> times faster than that for J=12. The optimal J value does not
> exceed 6 in any of the test runs. The benchmarks are run on a machine
> with 6 cores, with 2 threads per core, i.e, 12 hyperthreads in all.
>
> To improve performance, modify coccicheck to use at most only
> one thread per core by default.
>
> Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>

I have applied this one, so just the patch on the docuemtnation needs to
be improved.

julia

>
> ---
> Changes in V2:
> - Change commit message as suggested by Julia Lawall
> Changes in V3:
> - Use J/2 as optimal value for machines with more
> than 8 hyperthreads as well.
> ---
> scripts/coccicheck | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/scripts/coccicheck b/scripts/coccicheck
> index e04d328210ac..a72aa6c037ff 100755
> --- a/scripts/coccicheck
> +++ b/scripts/coccicheck
> @@ -75,8 +75,13 @@ else
> OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
> fi
>
> + # Use only one thread per core by default if hyperthreading is enabled
> + THREADS_PER_CORE=$(lscpu | grep "Thread(s) per core: " | tr -cd [:digit:])
> if [ -z "$J" ]; then
> NPROC=$(getconf _NPROCESSORS_ONLN)
> + if [ $THREADS_PER_CORE -gt 1 -a $NPROC -gt 2 ] ; then
> + NPROC=$((NPROC/2))
> + fi
> else
> NPROC="$J"
> fi
> --
> 2.25.1
>
> _______________________________________________
> Cocci mailing list
> Cocci@systeme.lip6.fr
> https://systeme.lip6.fr/mailman/listinfo/cocci
>

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