linux-kernel - Re: [RFC PATCH 2/4] sched: make schedstats helpers not depend on cfs

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Date:   Thu, 19 Nov 2020 19:24:31 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, juri.lelli@...hat.com,
        Vincent Guittot <vincent.guittot@...aro.org>,
        dietmar.eggemann@....com, Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>, bristot@...hat.com,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: [RFC PATCH 2/4] sched: make schedstats helpers not depend on cfs_rq

On Thu, Nov 19, 2020 at 3:45 PM Mel Gorman <mgorman@...e.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@...il.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