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

From: Mark Rutland <mark.rutland@arm.com>
To: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Andi Kleen <ak@linux.intel.com>, Kan Liang <kan.liang@intel.com>,
	Dmitri Prokhorov <Dmitry.Prohorov@intel.com>,
	Valery Cherepennikov <valery.cherepennikov@intel.com>,
	David Carrillo-Cisneros <davidcc@google.com>,
	Stephane Eranian <eranian@google.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi
Date: Mon, 19 Jun 2017 16:14:41 +0100	[thread overview]
Message-ID: <20170619151441.GB4555@leverpostej> (raw)
In-Reply-To: <f3890c43-c737-4d0a-4687-c1a5adb0e542@linux.intel.com>

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