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

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Message-ID: <1084da08-f67d-b5d7-add4-580e9246b7b7@molgen.mpg.de>
Date:   Thu, 24 Feb 2022 09:24:11 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
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

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@...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?

You are right. I guess with 1/2 I just wanted to document clearly, what 
I learned in #sed@....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
>>