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Subject: Re: [V2] perf/core: Avoid calling perf_mux_hrtimer_restart multiple
 times when scheduling event groups
From:   Athira Rajeev <atrajeev@linux.vnet.ibm.com>
In-Reply-To: <YW1ViqOYaVi8NnqE@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Oct 2021 17:52:10 +0530
Cc:     Song Liu <songliubraving@fb.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "maddy@linux.vnet.ibm.com" <maddy@linux.vnet.ibm.com>,
        "kjain@linux.ibm.com" <kjain@linux.ibm.com>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "eranian@google.com" <eranian@google.com>
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Message-Id: <EF5305ED-4A51-48D5-AB89-7E4A32DD3E7A@linux.vnet.ibm.com>
References: <20211015070403.4809-1-atrajeev@linux.vnet.ibm.com>
 <6E561141-B584-4DB8-A33E-BCD3FF572FA4@fb.com>
 <YW1ViqOYaVi8NnqE@hirez.programming.kicks-ass.net>
To:     Peter Zijlstra <peterz@infradead.org>
Precedence: bulk


> On 18-Oct-2021, at 4:37 PM, Peter Zijlstra <peterz@infradead.org> =
wrote:
>=20
> On Sat, Oct 16, 2021 at 01:08:04AM +0000, Song Liu wrote:
>>=20
>>=20
>>> On Oct 15, 2021, at 12:04 AM, Athira Rajeev =
<atrajeev@linux.vnet.ibm.com> wrote:
>>>=20
>>> 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".
>>>=20
>>> 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.
>>>=20
>>> Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
>>=20
>> Acked-by: Song Liu <song@kernel.org>
>=20
> 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.=