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

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Date:   Tue, 24 Oct 2017 14:59:44 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
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


* 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

etc.

Is this how you implemented it?

If the threads in the thread pool are just free-running then the scheduler might 
not migrate it to the 'right' CPU that is streaming the perf events and there will 
be a lot of cross-talking between CPUs.

Inherited events (default 'perf record') is tougher.

Thanks,

	Ingo