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

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Message-ID: <YW1ViqOYaVi8NnqE@hirez.programming.kicks-ass.net>
Date:   Mon, 18 Oct 2021 13:07:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     Athira Rajeev <atrajeev@...ux.vnet.ibm.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 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!