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

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Date:   Tue, 24 Oct 2017 15:25:23 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, "Liang, Kan" <kan.liang@...el.com>,
        "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


* Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Em Tue, Oct 24, 2017 at 02:59:44PM +0200, Ingo Molnar escreveu:
> > 
> > * Jiri Olsa <jolsa@...hat.com> wrote:
> > 
> > > 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:
> > 
> > So, in the context of system-wide profiling, the way that would work best I think 
> > is the following:
> > 
> >   thread #0 binds itself to CPU#0 (via sched_setaffinity) and creates a per-CPU event on CPU#0
> >   thread #1 binds itself to CPU#1 (via sched_setaffinity) and creates a per-CPU event on CPU#1
> >   thread #2 binds itself to CPU#2 (via sched_setaffinity) and creates a per-CPU event on CPU#2
> 
> Right, that is how I think it should be done as well, and those will
> just dump on separate files, in a per session directory, with an extra
> file for the session details, in what is now the header.

Yes. Also note how easy to examine such a directory structure is - I'd suggest 
making all the session details textual eventually. I.e. only the ring-buffers 
should be binary, the rest should be arch-independent text encoding.

It's also very extensible.

> Later, the same thing happens at processing time, this time we'll have
> contention to access global thread state, the need for rounds of
> PERF_SAMPLE_TIME based ordering, like what we have now in the
> tools/perf/util/ordered-events.[ch] code, etc.
> 
> This works for both 'report', 'script', 'top', 'trace', etc, as is
> basically the model we already have. All the work that was done for
> refcounting the thread, map, etc as well as locking those rbtrees would
> finally be taken full advantage of.

Yeah, cool!

Thanks,

	Ingo