linux-kernel - Re: [PATCH] perf test: Fix fails of perf stat --bpf-counters --for-each-cgroup on s390

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Message-ID: <7451a263-82e8-4daa-a7f6-009d5560445e@linux.ibm.com>
Date:   Fri, 8 Dec 2023 12:29:51 +0100
From:   Thomas Richter <tmricht@...ux.ibm.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org, svens@...ux.ibm.com, gor@...ux.ibm.com,
        sumanthk@...ux.ibm.com, hca@...ux.ibm.com
Subject: Re: [PATCH] perf test: Fix fails of perf stat --bpf-counters
 --for-each-cgroup on s390

On 12/8/23 12:07, Thomas Richter wrote:
> On 12/8/23 00:26, Namhyung Kim wrote:
> 
>> Thanks for the patch.  But I think it should support
>> machines without systemd (or maybe with old versions).
>>
>> Also probably you want to reset the behavior after
>> the test.  I think we can just run some built-in test
>> workload like `perf test -w thloop`.
>>
>> Thanks,
>> Namhyung
> 
> Thanks for our feedback.
> Well regarding the use of systemd daemon-reexec the manual says
> this command restarts the systemd triggered processes.
> There is nothing to reset. All ports stay active while the command
> is processed.
> 
> I tried your 'perf test -w thloop`, but that did not trigger
> anything on system.slice.
> 
> I do not understand enough about cgroups and system.slice, but I am
> under the impression, that the system.slice just increment counters
> when executed by processes under systemd control. Maybe I am wrong.
> 
> The only other workload which always incremented system.slice counters
> was 'ssh localhost ls -l', which involves local login and a running sshd.
> 
> Thanks for your advice on how to continue on this.
> 
> 

I have done some reading and found this:
Special Slice Units
There are four ".slice" units which form the basis of the hierarchy for assignment of 
resources for services, users, and virtual machines or containers. 
See systemd.slice(7) for details about slice units.

-.slice
The root slice is the root of the slice hierarchy. It usually does not contain units directly,
but may be used to set defaults for the whole tree.
Added in version 206.

system.slice
By default, all system services started by systemd are found in this slice.
Added in version 206.

So it looks like system.slice attached counters get only incremented
when systemd controlled processes do some work,

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
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