linux-kernel - Re: [RFC PATCH v2 3/5] sched: make schedstats helper independent of cfs

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Date:   Tue, 24 Nov 2020 21:08:09 +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 <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <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 v2 3/5] sched: make schedstats helper independent of cfs_rq

On Tue, Nov 24, 2020 at 7:40 PM Mel Gorman <mgorman@...e.de> wrote:
>
> On Mon, Nov 23, 2020 at 08:58:06PM +0800, Yafang Shao wrote:
> > The 'cfs_rq' in these helpers
> > update_stats_{wait_start, wait_end, enqueue_sleeper} is only used to get
> > the rq_clock, so we can pass the rq directly. Then these helpers can be
> > used by all sched class after being moved into stats.h.
> >
> > After that change, the size of vmlinux is increased around 824Bytes.
> >                       w/o this patch, with this patch
> > Size of vmlinux:      78443832        78444656
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
>
> The inline helpers are quite large. When I was suggesting that the overhead
> was minimal, what I expected what that the inline functions would be a
> schedstat_enabled() followed by a real function call. It would introduce
> a small additional overhead when schedstats are enabled but avoid vmlinux
> growing too large
>
> e.g.
>
> static inline void
> update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
> {
>         if (!schedstat_enabled())
>                 return;
>
>         __update_stats_wait_start(cfs_rq, se);
> }
>
> where __update_stats_wait_start then lives in kernel/sched/stats.c
>

Good idea!  Now I understand what you mean. Thanks for the detailed explanation.
I will update it in the next version.


-- 
Thanks
Yafang