linux-kernel - Re: [PATCH V3 0/6] event synthesization multithreading for perf record

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Date:   Tue, 24 Oct 2017 13:47:55 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "wangnan0@...wei.com" <wangnan0@...wei.com>,
        "hekuang@...wei.com" <hekuang@...wei.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH V3 0/6] event synthesization multithreading for perf
 record

On Tue, Oct 24, 2017 at 11:22:00AM +0200, Ingo Molnar wrote:
> 
> * Liang, Kan <kan.liang@...el.com> wrote:
> 
> > For 'all', do you mean the whole process?
> 
> Yeah.
> 
> > I think that's the ultimate goal.  Eventually there will be per-CPU recording
> > threads created at the beginning of perf record and go through the whole process.
> > The plan is to do the multithreading step by step from the simplest case.
> > Synthesizing stage is just a start.
> 
> So, why not do it like the kernel did: add all the threads, create the percpu 
> files, and introduce a 'big perf lock' (big mutex) that is taken for all the 
> current non-threaded perf functionality. This should be fairly straightforward to 
> do and should be 'obviously correct'.
> 
> _Then_ start doing the hard threading work on top of this, like threading the 
> synthesizing phase.
> 
> Doing the whole per CPU thread setup/teardown for just the synthesizing part of it 
> looks like the wrong design.
> 
> I.e. what I'm suggesting is no extra threading work, just organizing it in a 
> different fashion and increasing the life-time of the per CPU threads from 'perf 
> startup' to 'perf shutdown'.

I recently made some changes on threaded record, which are based
on Namhyungs time* API, which is needed to read/sort the data afterwards

but I wasn't able to get any substantial and constant reduce of LOST events
and then I got sidetracked and did not finish, but it's in here:

git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git perf/data

I'll try to rebase and send it out for comments

jirka