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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Date:   Mon, 19 Jun 2017 14:26:52 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...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

On Mon, Jun 19, 2017 at 04:08:32PM +0300, Alexey Budankov wrote:
> On 16.06.2017 1:10, Alexey Budankov wrote:
> >On 15.06.2017 22:56, Mark Rutland wrote:
> >>On Thu, Jun 15, 2017 at 08:41:42PM +0300, Alexey Budankov wrote:
> >>>This series of patches continues v2 and addresses captured comments.

> >>>Specifically this patch replaces pinned_groups and flexible_groups
> >>>lists of perf_event_context by red-black cpu indexed trees avoiding
> >>>data structures duplication and introducing possibility to iterate
> >>>event groups for a specific CPU only.

> >>Have you thrown Vince's perf fuzzer at this?
> >>
> >>If you haven't, please do. It can be found in the fuzzer directory of:
> >>
> >>https://github.com/deater/perf_event_tests
> >
> >Accepted.
> 
> I run the test suite and it revealed no additional regressions in
> comparison to what I have on the clean kernel.
> 
> However the fuzzer constantly reports some strange stacks that are
> not seen on the clean kernel and I have no idea how that might be
> caused by the patches.

Ok; that was the kind of thing I was concerned about.

What you say "strange stacks", what do you mean exactly?

I take it the kernel spewing backtraces in dmesg?

Can you dump those?

Thanks,
Mark.