linux-kernel - Re: [PATCH RFC V2 00/10] perf top optimization

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Date:   Tue, 19 Sep 2017 11:24:05 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH RFC V2 00/10] perf top optimization

Em Tue, Sep 19, 2017 at 12:39:47PM +0000, Liang, Kan escreveu:
> > On Mon, Sep 18, 2017 at 10:01:00AM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Mon, Sep 18, 2017 at 10:57:08AM +0200, Jiri Olsa escreveu:
> > > > he proposed solution and it was changed&posted by Arnaldo in here:

> > > >   https://marc.info/?l=linux-kernel&m=149132267410294&w=2

> > > > but looks like it never got merged

> > > > could you please add this or similar code before you add the locking
> > > > code/overhead in?

> > > I'm rehashing that patch and adding it on top of what is in my
> > > perf/core branch, will push soon, for now you can take a look at
> > tmp.perf/core.

> > checked the code.. one nit, could we have single threaded by default?
> > only one command is multithreaded atm, it could call perf_set_multihreaded
> > instead of all current related commands call perf_set_singlethreaded

> I agree with single threaded as default setting, also I think we need both
> functions, perf_set_multihreaded and perf_set_singlethreaded.
> Perf tools probably be half single threaded and half multithreaded.
> E.g. the perf top optimization. Only the events synthesize codes are
> multithreaded. So we have to set multithreaded first, then change it
> to single threaded.

Ok, agreed with both of you, i.e. I'll make it single threaded by
default, and provide both functions, this way we get a default that is
what most tools use, and a way to select multithreaded mode for when it
is needed, then going back to single threaded.

- Arnaldo