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From:   Paul Menzel <pmenzel@molgen.mpg.de>
To:     "Paul E. McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Shuah Khan <shuah@kernel.org>
Cc:     Paul Menzel <pmenzel@molgen.mpg.de>,
        Zhouyi Zhou <zhouzhouyi@gmail.com>, rcu@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 2/2] torture: Make thread detection more robust by using lspcu
Date:   Tue, 22 Feb 2022 13:07:17 +0100
Message-Id: <20220222120718.17141-2-pmenzel@molgen.mpg.de>
In-Reply-To: <20220222120718.17141-1-pmenzel@molgen.mpg.de>
References: <20220222120718.17141-1-pmenzel@molgen.mpg.de>
MIME-Version: 1.0
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For consecutive numbers *lscpu* collapses the output and just shows the
range with start and end. The processors are numbered that way on POWER8.

    $ sudo ppc64_cpu --smt=8
    $ lscpu | grep '^NUMA node'
    NUMA node(s):                    2
    NUMA node0 CPU(s):               0-79
    NUMA node8 CPU(s):               80-159

This causes the heuristic to detect the number threads per core, looking
for the number after the first comma, to fail, and QEMU aborts because of
invalid arguments.

    $ lscpu | sed -n -e '/^NUMA node0/s/^[^,]*,\([0-9]*\),.*$/\1/p'
    $

(Before the last patch, the whole line was returned.)

    $ lscpu | grep '^NUMA node0' | sed -e 's/^[^,-]*(,|\-)\([0-9]*\),.*$/\1/'
    NUMA node0 CPU(s):               0-79

*lscpu* shows the number of threads per core, so use that value directly.

    $ sudo ppc64_cpu --smt=8
    $ lscpu | grep 'Thread(s) per core'
    Thread(s) per core:              8
    $ sudo ppc64_cpu --smt=off
    $ lscpu | grep 'Thread(s) per core'
    Thread(s) per core:              1

Note, the replaced heuristic is also incorrect for that case, where the
threads per core are disabled.

    $ lscpu | sed -n -e '/^NUMA node0/s/^[^,]*,\([0-9]*\),.*$/\1/p'
    8

Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
---
 tools/testing/selftests/rcutorture/bin/functions.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rcutorture/bin/functions.sh b/tools/testing/selftests/rcutorture/bin/functions.sh
index 5cff520955e6..66d0414d8e4b 100644
--- a/tools/testing/selftests/rcutorture/bin/functions.sh
+++ b/tools/testing/selftests/rcutorture/bin/functions.sh
@@ -301,7 +301,7 @@ specify_qemu_cpus () {
 			echo $2 -smp $3
 			;;
 		qemu-system-ppc64)
-			nt="`lscpu | sed -n -e '/^NUMA node0/s/^[^,]*,\([0-9]*\),.*$/\1/p'`"
+			nt="`lscpu | sed -n 's/^Thread(s) per core:\s*//p'`"
 			echo $2 -smp cores=`expr \( $3 + $nt - 1 \) / $nt`,threads=$nt
 			;;
 		esac
-- 
2.35.1