linux-kernel - Re: [PATCH v5 4/4]: perf/core: complete replace of lists by rb trees for pinned and flexible groups at perf_event

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Message-ID: <b5f616ad-1dd9-c66a-96f0-75b9489ae099@linux.intel.com>
Date:   Tue, 18 Jul 2017 16:38:26 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Andi Kleen <ak@...ux.intel.com>, Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/4]: perf/core: complete replace of lists by rb trees
 for pinned and flexible groups at perf_event_context

Hi,

On 18.07.2017 14:33, Alexander Shishkin wrote:
> Alexey Budankov <alexey.budankov@...ux.intel.com> writes:
> 
>> Hi,
> 
> Hi,
> 
>> Are there any new comments so far? Could you please suggest further steps forward?
> 
> Apparently the patches are not threaded, so one needs to fish them out
> one by one in order to review.

Thanks for feedback. The BKM in this case is just to keep subject unchanged, right?

> 
>> On 10.07.2017 16:03, Alexey Budankov wrote:
>>> perf/core: complete replace of lists by rb trees for pinned and 
>>>            flexible groups at perf_event_context
> 
> No need to duplicate the subject line here. Also, it can be more concise
> than this like "perf: Replace context's pinned/flexible lists with trees".
> 
>>> By default, the userspace perf tool opens per-cpu task-bound events
>>> when sampling, so for N logical events requested by the user, the tool
>>> will open N * NR_CPUS events.
>>>
>>> In the kernel, we mux events with a hrtimer, periodically rotating the
>>> flexible group list and trying to schedule each group in turn. We skip
>>> groups whose cpu filter doesn't match. So when we get unlucky, we can
>>> walk N * (NR_CPUS - 1) groups pointlessly for each hrtimer invocation.
>>>
>>> This has been observed to result in significant overhead when running
>>> the STREAM benchmark on 272 core Xeon Phi systems.
>>>
>>> One way to avoid this is to place our events into an rb tree sorted by
>>> CPU filter, so that our hrtimer can skip to the current CPU's
>>> list and ignore everything else.
> 
> It looks like these 4 paragraphs are repeated in every patch.
> 
>>> This patch implements complete replacement of lists by rb trees for 
>>> pinned and flexible groups.
> 
> And this is the actually informative part.
> 
>>> The patch set was tested on Xeon Phi using perf_fuzzer and tests 
>>> from here: https://github.com/deater/perf_event_tests
> 
> Although this is also useful.
> 
>>> The full patch set (v1-4) is attached for convenience. 
>>>
>>> Branch revision:
>>> * perf/core 007b811b4041989ec2dc91b9614aa2c41332723e 
>>>   Merge tag 'perf-core-for-mingo-4.13-20170719' of 
>>>   git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core
> 
> Not sure what this is, though.

Just mentioned branch and revision when forking local development branch.
Considered it helpful for applying the whole patch set.

> 
> As has been recently pointed out elsewhere, you can get a good idea of
> how to structure and format commit messages for a particular piece of
> code by looking at 'git log path/to/code' and paying attention to common
> patterns.
> 
> Thanks,
> --
> Alex
> 

Thanks,
Alexey