linux-kernel - Re: [PATCH v8 10/22] perf record: Introduce --threads=<spec> command line option

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Date:   Thu, 1 Jul 2021 21:14:17 +0300
From:   "Bayduraev, Alexey V" <alexey.v.bayduraev@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Antonov <alexander.antonov@...ux.intel.com>,
        Alexei Budankov <abudankov@...wei.com>,
        Riccardo Mancini <rickyman7@...il.com>
Subject: Re: [PATCH v8 10/22] perf record: Introduce --threads=<spec> command
 line option

Hi,

On 01.07.2021 17:26, Arnaldo Carvalho de Melo wrote:
> Em Thu, Jul 01, 2021 at 02:50:40PM +0300, Bayduraev, Alexey V escreveu:
>> On 30.06.2021 21:54, Bayduraev, Alexey V wrote:
>>> On 30.06.2021 20:28, Arnaldo Carvalho de Melo wrote:
>>>> I thought you would start with plain:
> 
>>>>   -j N
> 
>>>> And start one thread per CPU in 'perf record' existing CPU affinity
>>>> mask, then go on introducing more sophisticated modes.
> 
>>> As I remember the first prototype [1] and 
>>> [2] https://lore.kernel.org/lkml/20180913125450.21342-1-jolsa@kernel.org/
> 
>>> introduces: 
> 
>>> --thread=mode|number_of_threads
> 
>>> where mode defines cpu masks (cpu/numa/socket/etc)
> 
>>> Then somewhere while discussing this patchset it was decided, for unification,
>>> that --thread should only define CPU/affinity masks or their aliases.
>>> I think Alexei or Jiri could clarify this more.
> 
>>>> Have you done this way because its how VTune has evolved over the years
>>>> and now expects from 'perf record'?
> 
>>> VTune uses only --thread=cpu or no threading.
> 
>> However we would like to have such sophisticated cpu/affinity masks to
>> tune perf-record for different workloads.
> 
> I don't have, a priori, anything against the modes you propose, as you
> have a justification for them, its just how we should introduce that.
> 
> I.e. first doing the simple case of '-j NCPUS' and then doing what you
> need, so that we get more granular patches.
> 
> Not adding too much complexity per patch pays off when/if we find bugs
> and need to bisect.

This is a good idea, especially since this 10/22 patch is the most complex
patch in the patchset. I also think we can keep this simple -threads=NCPUS
form along with the -threads=masks option.

Regards,
Alexey

> 
>> For example, some HPC workloads prefer "numa" mask or most of telecom
>> workloads disallow to use cpus where their non-preemtable
>> communication threads work.
> 
> - Arnaldo
>