linux-kernel - Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi

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Message-ID: <20170619145908.GA23705@tassilo.jf.intel.com>
Date:   Mon, 19 Jun 2017 07:59:08 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during
 per-process profiling of STREAM benchmark on Intel Xeon Phi

> > For comparison, can you give --per-thread a go prior to these patches
> > being applied?
> 
> FWIW, I had a go with (an old) perf record on an arm64 system using
> --per-thread, and I see that no samples are recorded, which seems like a
> bug.
> 
> With --per-thread, the slwodown was ~20%, whereas with the defaults it
> was > 400%.

I'm not sure what the point of the experiment is? It has to work
with reasonable overead even without --per-thread.

FWIW Alexey already root caused the problem, so there's no need
to restart the debugging.

-Andi