From: Julia Lawall <julia.lawall@inria.fr>
To: Sumera Priyadarsini <sylphrenadin@gmail.com>
Cc: michal.lkml@markovi.net, Gilles.Muller@lip6.fr,
gregkh@linuxfoundation.org, nicolas.palix@imag.fr,
linux-kernel@vger.kernel.org, cocci@systeme.lip6.fr
Subject: Re: [Cocci] [PATCH] scripts: coccicheck: Change default value for parallelism
Date: Wed, 12 Aug 2020 22:15:04 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.22.394.2008122211330.2468@hadrien> (raw)
In-Reply-To: <20200812182722.4553-1-sylphrenadin@gmail.com>
On Wed, 12 Aug 2020, Sumera Priyadarsini wrote:
> By default, coccicheck utilizes all available threads to implement
> parallelisation. However, when hyperthreading is enabled, this leads
> to all threads per core being occupied resulting in longer wall-clock
> times and higher power consumption.
I have the feeling that the above sentence is not quite optimal.
Actually, using all of the available hardware threads would not be a bad
thing, if it was giving a benefit. The point is that it doesn't. It
makes the performance worse instead.
> Hence, to improve performance,
> modify coccicheck to use only one thread per core atmost.
"atmost" is not a word. It would be clearer to say "to use at most one
thread per core".
> In the cases where the total number of threads is more than 8 and
> hyperthreading is enabled, it was observed that optimum performance
> is achieved around one-fourth of the total number of cores.
> Modify the script further to accommodate this use case.
It would be nice to give some performance numbers and some information
about the machine used.
thanks,
julia
>
> Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>
> ---
> scripts/coccicheck | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/scripts/coccicheck b/scripts/coccicheck
> index e04d328210ac..dd228dcc915e 100755
> --- a/scripts/coccicheck
> +++ b/scripts/coccicheck
> @@ -75,8 +75,17 @@ 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
> + if [ $NPROC -gt 8 ] ; then
> + NPROC=$((NPROC/4))
> + else
> + NPROC=$((NPROC/2))
> + fi
> + fi
> else
> NPROC="$J"
> fi
> --
> 2.17.1
>
> _______________________________________________
> Cocci mailing list
> Cocci@systeme.lip6.fr
> https://systeme.lip6.fr/mailman/listinfo/cocci
>
next prev parent reply other threads:[~2020-08-12 20:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 18:27 Sumera Priyadarsini
2020-08-12 20:15 ` Julia Lawall [this message]
[not found] ` <CACAkLuqo+CJeyvVZ0oaN=6SqQNxXinfv8t6FNPyORO=GCCvstA@mail.gmail.com>
2020-08-13 10:57 ` [Cocci] " Julia Lawall
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