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 18:27:17 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Mark Rutland <mark.rutland@....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 19.06.2017 18:14, Mark Rutland wrote:
> 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?

v4.12-rc4+,
perf/core d0fabd1 [origin/perf/core] perf/core: Remove unused 
perf_cgroup_event_cgrp_time() function

> 
> Thanks,
> Mark
>