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 16:14:41 +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 04:37:41PM +0300, Alexey Budankov wrote:
> On 19.06.2017 16:26, Mark Rutland wrote:
> >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?
> 
> Here it is:
> 
> list_del corruption. prev->next should be ffff88c2c4654010, but was
> ffff88c31eb0c020
> [  607.632813] ------------[ cut here ]------------
> [  607.632816] kernel BUG at lib/list_debug.c:53!

> [  607.635531] Call Trace:
> [  607.635583]  list_del_event+0x1d7/0x210

Given this patch changes how list_{del,add}_event() works, it's possible
that this is a new bug.

I was going to try to test this on arm64, but I couldn't get the patch
to apply. I had a go with v4.12-rc5, tip/perf/core, and tip/perf/urgent.

Which branch should I be using as the base?

Thanks,
Mark