linux-kernel - Re: [PATCH 2/2] torture: Make thread detection more robust by using lspcu

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Date:   Tue, 22 Feb 2022 09:43:28 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Zhouyi Zhou <zhouzhouyi@...il.com>, rcu@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] torture: Make thread detection more robust by using
 lspcu

On Tue, Feb 22, 2022 at 01:07:17PM +0100, Paul Menzel wrote:
> 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@...gen.mpg.de>

Makes sense, and thank you for chasing this down and for the fix!

But should this patch and 1/2 be merged?  Or am I confused and they
are somehow affecting two different lines of scripting?

							Thanx, Paul

> ---
>  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
>