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SubjectRe: [PATCH 2/2] torture: Make thread detection more robust by using lspcu
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Dear Paul,


Am 22.02.22 um 18:43 schrieb Paul E. McKenney:
> 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@molgen.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?

You are right. I guess with 1/2 I just wanted to document clearly, what
I learned in #sed@irc.libera.chat, that means, how to avoid using grep,
when sed is used.


Kind regards,

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
>>

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