linux-kernel - Re: [PATCH v7] perf: Sharing PMU counters across compatible events

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Date:   Mon, 25 Nov 2019 09:39:49 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     open list <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        David Carrillo Cisneros <davidca@...com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>, "Tejun Heo" <tj@...nel.org>
Subject: Re: [PATCH v7] perf: Sharing PMU counters across compatible events



> On Nov 24, 2019, at 11:22 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Fri, Nov 22, 2019 at 07:50:06PM +0000, Song Liu wrote:
>> 
>> 
>>> On Nov 22, 2019, at 11:33 AM, Jiri Olsa <jolsa@...hat.com> wrote:
>>> 
>>> On Fri, Nov 15, 2019 at 03:55:04PM -0800, Song Liu wrote:
>>>> This patch tries to enable PMU sharing. When multiple perf_events are
>>>> counting the same metric, they can share the hardware PMU counter. We
>>>> call these events as "compatible events".
>>>> 
>>>> The PMU sharing are limited to events within the same perf_event_context
>>>> (ctx). When a event is installed or enabled, search the ctx for compatible
>>>> events. This is implemented in perf_event_setup_dup(). One of these
>>>> compatible events are picked as the master (stored in event->dup_master).
>>>> Similarly, when the event is removed or disabled, perf_event_remove_dup()
>>>> is used to clean up sharing.
>>>> 
>>>> A new state PERF_EVENT_STATE_ENABLED is introduced for the master event.
>>>> This state is used when the slave event is ACTIVE, but the master event
>>>> is not.
>>>> 
>>>> On the critical paths (add, del read), sharing PMU counters doesn't
>>>> increase the complexity. Helper functions event_pmu_[add|del|read]() are
>>>> introduced to cover these cases. All these functions have O(1) time
>>>> complexity.
>>>> 
>>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>>> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
>>>> Cc: Jiri Olsa <jolsa@...nel.org>
>>>> Cc: Alexey Budankov <alexey.budankov@...ux.intel.com>
>>>> Cc: Namhyung Kim <namhyung@...nel.org>
>>>> Cc: Tejun Heo <tj@...nel.org>
>>>> Signed-off-by: Song Liu <songliubraving@...com>
>>>> 
>>>> ---
>>>> Changes in v7:
>>>> Major rewrite to avoid allocating extra master event.
>>> 
>>> hi,
>>> what is this based on? I can't apply it on tip/master:
>>> 
>>> 	Applying: perf: Sharing PMU counters across compatible events
>>> 	error: patch failed: include/linux/perf_event.h:722
>>> 	error: include/linux/perf_event.h: patch does not apply
>>> 	Patch failed at 0001 perf: Sharing PMU counters across compatible events
>>> 	hint: Use 'git am --show-current-patch' to see the failed patch
>>> 	When you have resolved this problem, run "git am --continue".
>>> 	If you prefer to skip this patch, run "git am --skip" instead.
>>> 	To restore the original branch and stop patching, run "git am --abort".
>> 
> 
> hi,
> I'm getting warning below when running 'perf test',
> not sure what's the reason yet..

Thanks for the heads-up. I will try to look into it. I am on vacation this 
week, so please expect some delay. 

Best,
Song