linux-kernel - Re: [V2] perf/core: Avoid calling perf_mux_hrtimer_restart multiple times when scheduling event groups

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Date:   Thu, 21 Oct 2021 17:52:10 +0530
From:   Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Song Liu <songliubraving@...com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "maddy@...ux.vnet.ibm.com" <maddy@...ux.vnet.ibm.com>,
        "kjain@...ux.ibm.com" <kjain@...ux.ibm.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "eranian@...gle.com" <eranian@...gle.com>
Subject: Re: [V2] perf/core: Avoid calling perf_mux_hrtimer_restart multiple
 times when scheduling event groups



> On 18-Oct-2021, at 4:37 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Sat, Oct 16, 2021 at 01:08:04AM +0000, Song Liu wrote:
>> 
>> 
>>> On Oct 15, 2021, at 12:04 AM, Athira Rajeev <atrajeev@...ux.vnet.ibm.com> wrote:
>>> 
>>> Perf uses multiplexing if there are more events to be scheduled than the
>>> available counters. With multiplexing, event groups will be rotated at
>>> specified interval of time which is set using "hrtimer". During event
>>> scheduling, if any of the event group fails to schedule, multiplexing
>>> gets enabled by setting "rotate_necessary" for that event context and
>>> starting the hrtimer by calling "perf_mux_hrtimer_restart".
>>> 
>>> Patch adds an optimisation to avoid calling "perf_mux_hrtimer_restart"
>>> multiple times if already rotate_necessary is set for that context.
>>> Even though "perf_mux_hrtimer_restart" will just return if hrtimer is
>>> already active, this could avoid the overhead of calling this function
>>> multiple times if there are many event groups. Patch adds the check to
>>> avoid calling perf_mux_hrtimer_restart() for each event group on
>>> every schedule.
>>> 
>>> Signed-off-by: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
>> 
>> Acked-by: Song Liu <song@...nel.org>
> 
> Thanks!

Thanks for checking the patch.

Hi Peterz,
Should I resend this patch with Acked-by or can you consider pulling it, if the patch looks fine to you.

Thanks
Athira.