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

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Date:   Mon, 18 Sep 2017 10:57:08 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...el.com
Cc:     acme@...nel.org, 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 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?

thanks,
jirka