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From:   Song Liu <songliubraving@fb.com>
To:     Athira Rajeev <atrajeev@linux.vnet.ibm.com>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "mingo@redhat.com" <mingo@redhat.com>,
        "eranian@google.com" <eranian@google.com>
Subject: Re: [V2] perf/core: Avoid calling perf_mux_hrtimer_restart multiple
 times when scheduling event groups
Thread-Topic: [V2] perf/core: Avoid calling perf_mux_hrtimer_restart multiple
 times when scheduling event groups
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Date:   Sat, 16 Oct 2021 01:08:04 +0000
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References: <20211015070403.4809-1-atrajeev@linux.vnet.ibm.com>
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> On Oct 15, 2021, at 12:04 AM, Athira Rajeev <atrajeev@linux.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@linux.vnet.ibm.com>

Acked-by: Song Liu <song@kernel.org>