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

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Message-ID: <20171025090034.GA27028@krava>
Date:   Wed, 25 Oct 2017 11:00:34 +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 02:59:44PM +0200, Ingo Molnar wrote:
> 
> * 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?

in a way ;-) but I made it more generic and let record create just
few threads and let them share cpu subset.. and so there was no binding

> 
> 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.

ok it's easy to add binding now and 1:1 thread:cpu mapping.. I'll retry

jirka