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;
MIME-Version: 1.0
References: <20201119035230.45330-1-laoar.shao@gmail.com> <20201119035230.45330-3-laoar.shao@gmail.com>
 <20201119074539.GE3306@suse.de>
In-Reply-To: <20201119074539.GE3306@suse.de>
From:   Yafang Shao <laoar.shao@gmail.com>
Date:   Thu, 19 Nov 2020 19:24:31 +0800
Message-ID: <CALOAHbDf1V6Fo3HBvMOWYckSxjUsfpxn+aePgUtjLxKf7dTgGw@mail.gmail.com>
Subject: Re: [RFC PATCH 2/4] sched: make schedstats helpers not depend on cfs_rq
To:     Mel Gorman <mgorman@suse.de>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, juri.lelli@redhat.com,
        Vincent Guittot <vincent.guittot@linaro.org>,
        dietmar.eggemann@arm.com, Steven Rostedt <rostedt@goodmis.org>,
        Benjamin Segall <bsegall@google.com>, bristot@redhat.com,
        LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Nov 19, 2020 at 3:45 PM Mel Gorman <mgorman@suse.de> wrote:
>
> On Thu, Nov 19, 2020 at 11:52:28AM +0800, Yafang Shao wrote:
> > The 'cfs_rq' in these helpers is only used to get the rq_clock, so we
> > can pass the rq_clock directly. After that, these helpers can be used by
> > all sched class.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
>
> This introduces overhead in the general case even when schedstats is
> disabled. Previously, update_stats_wait_start was a static inline so
> function call overhead was avoided and schedstat_enabled() meant the
> overhead was negligible. As it's now a function call, the cost of the
> function entry/exit will be unconditionally hit regardless of intrest
> in schedstat.
>
> Regardless of the merit of adding schedstats for RT, the overhead of
> schedstats when stats are disabled should remain the same with the
> static branch check done in an inline function.
>

Thanks for the explanation.
I will make them inline in the next version.


-- 
Thanks
Yafang