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

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Date:   Tue, 19 Sep 2017 10:19:01 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     kan.liang@...el.com, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, jolsa@...nel.org,
        namhyung@...nel.org, adrian.hunter@...el.com,
        lukasz.odzioba@...el.com, ak@...ux.intel.com
Subject: Re: [PATCH RFC V2 00/10] perf top optimization

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:
> > On Sun, Sep 10, 2017 at 07:23:13PM -0700, kan.liang@...el.com wrote:
> > > From: Kan Liang <kan.liang@...el.com>
> > > 
> > > The patch series intends to fix the severe performance issue in
> > > Knights Landing/Mill, when monitoring in heavy load system.
> > > perf top costs a few minutes to show the result, which is
> > > unacceptable.
> > > With the patch series applied, the latency will reduces to
> > > several seconds.
> > > 
> > > machine__synthesize_threads and perf_top__mmap_read costs most of
> > > the perf top time (> 99%).
> > 
> > looks like this patchset adds locking into code paths
> > used by other single threaded tools and that might
> > be bad for them as noted by Andi in here:
> > 
> >   https://marc.info/?l=linux-kernel&m=149031672928989&w=2
> > 
> > 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

other than that it looks ok

thanks,
jirka