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From: Sumera Priyadarsini <sylphrenadin@gmail.com>
To: Julia.Lawall@lip6.fr
Cc: corbet@lwn.net, michal.lkml@markovi.net, Gilles.Muller@lip6.fr,
	linux-doc@vger.kernel.org, nicolas.palix@imag.fr,
	linux-kernel@vger.kernel.org, cocci@systeme.lip6.fr
Subject: [Cocci] [PATCH 1/2] scripts: coccicheck: Change default value for parallelism
Date: Thu, 24 Sep 2020 16:56:08 +0530
Message-ID: <3beb97122995eafe3f0b831e36167b1edadb47c5.1600945451.git.sylphrenadin@gmail.com> (raw)
In-Reply-To: <cover.1600945451.git.sylphrenadin@gmail.com>

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>

---
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

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Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-24 11:23 [Cocci] [PATCH 0/2] Improve Coccinelle Parallelisation Sumera Priyadarsini
2020-09-24 11:26 ` Sumera Priyadarsini [this message]
2020-09-27 20:55   ` [Cocci] [PATCH 1/2] scripts: coccicheck: Change default value for parallelism Julia Lawall
2020-09-24 11:27 ` [Cocci] [PATCH 2/2] Documentation: Coccinelle: Modify parallelisation information in docs Sumera Priyadarsini
2020-09-27 20:55   ` Julia Lawall

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