Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 18 Oct 2021 13:07:54 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Song Liu <songliubraving@fb.com>
Cc:     Athira Rajeev <atrajeev@linux.vnet.ibm.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>
Subject: Re: [V2] perf/core: Avoid calling perf_mux_hrtimer_restart multiple
 times when scheduling event groups
Message-ID: <YW1ViqOYaVi8NnqE@hirez.programming.kicks-ass.net>
References: <20211015070403.4809-1-atrajeev@linux.vnet.ibm.com>
 <6E561141-B584-4DB8-A33E-BCD3FF572FA4@fb.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <6E561141-B584-4DB8-A33E-BCD3FF572FA4@fb.com>
Precedence: bulk

On Sat, Oct 16, 2021 at 01:08:04AM +0000, Song Liu wrote:
> 
> 
> > 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>

Thanks!