linux-kernel - Re: [PATCH v2 0/3] perf-stat: share hardware PMCs with BPF

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Date:   Tue, 23 Mar 2021 21:26:39 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v2 0/3] perf-stat: share hardware PMCs with BPF



> On Mar 23, 2021, at 2:10 PM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> 
> Em Fri, Mar 19, 2021 at 04:14:42PM +0000, Song Liu escreveu:
>>> On Mar 19, 2021, at 8:58 AM, Namhyung Kim <namhyung@...nel.org> wrote:
>>> On Sat, Mar 20, 2021 at 12:35 AM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
>>>> Em Fri, Mar 19, 2021 at 09:54:59AM +0900, Namhyung Kim escreveu:
>>>>> On Fri, Mar 19, 2021 at 9:22 AM Song Liu <songliubraving@...com> wrote:
>>>>>>> On Mar 18, 2021, at 5:09 PM, Arnaldo <arnaldo.melo@...il.com> wrote:
>>>>>>> On March 18, 2021 6:14:34 PM GMT-03:00, Jiri Olsa <jolsa@...hat.com> wrote:
>>>>>>>> On Thu, Mar 18, 2021 at 03:52:51AM +0000, Song Liu wrote:
>>>>>>>>> perf stat -C 1,3,5                  107.063 [sec]
>>>>>>>>> perf stat -C 1,3,5 --bpf-counters   106.406 [sec]
> 
>>>>>>>> I can't see why it's actualy faster than normal perf ;-)
>>>>>>>> would be worth to find out
> 
>>>>>>> Isn't this all about contended cases?
> 
>>>>>> Yeah, the normal perf is doing time multiplexing; while --bpf-counters
>>>>>> doesn't need it.
> 
>>>>> Yep, so for uncontended cases, normal perf should be the same as the
>>>>> baseline (faster than the bperf).  But for contended cases, the bperf
>>>>> works faster.
> 
>>>> The difference should be small enough that for people that use this in a
>>>> machine where contention happens most of the time, setting a
>>>> ~/.perfconfig to use it by default should be advantageous, i.e. no need
>>>> to use --bpf-counters on the command line all the time.
> 
>>>> So, Namhyung, can I take that as an Acked-by or a Reviewed-by? I'll take
>>>> a look again now but I want to have this merged on perf/core so that I
>>>> can work on a new BPF SKEL to use this:
> 
>>> I have a concern for the per cpu target, but it can be done later, so
> 
>>> Acked-by: Namhyung Kim <namhyung@...nel.org>
> 
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.bpf/bpf_perf_enable
> 
>>> Interesting!  Actually I was thinking about the similar too. :)
>> 
>> Hi Namhyung, Jiri, and Arnaldo,
>> 
>> Thanks a lot for your kind review. 
>> 
>> Here is updated 3/3, where we use perf-bench instead of stressapptest.
> 
> I had to apply this updated 3/3 manually, as there was some munging, its
> all now at:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.perf/core
> 
> Please take a look at the "Committer testing" section I added to the
> main patch, introducing bperf:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/commit/?h=tmp.perf/core&id=7fac83aaf2eecc9e7e7b72da694c49bb4ce7fdfc
> 
> And check if I made any mistake or if something else could be added.
> 
> It'll move to perf/core after my set of automated tests finishes.

Thanks Arnaldo! Looks great!

Song