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

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Message-ID: <YN3Qn5mO5cPffPZa@kernel.org>
Date:   Thu, 1 Jul 2021 11:26:39 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Bayduraev, Alexey V" <alexey.v.bayduraev@...ux.intel.com>
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

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.

> 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