linux-kernel - Re: [PATCH] sched/fair: Cleanup definition of NOHZ blocked load functions

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Message-ID: <CAKfTPtCq_TrG=rNoH=_H_KveWNV-k_bcSQVo2FcDUGhp3Pr--g@mail.gmail.com>
Date:   Mon, 3 Jun 2019 11:53:50 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, Qian Cai <cai@....pw>
Subject: Re: [PATCH] sched/fair: Cleanup definition of NOHZ blocked load functions

On Mon, 3 Jun 2019 at 11:38, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Sun, Jun 02, 2019 at 05:41:10PM +0100, Valentin Schneider wrote:
> > cfs_rq_has_blocked() and others_have_blocked() are only used within
> > update_blocked_averages(). The !CONFIG_FAIR_GROUP_SCHED version of the
> > latter calls them within a #define CONFIG_NO_HZ_COMMON block, whereas
> > the CONFIG_FAIR_GROUP_SCHED one calls them unconditionnally.
> >
> > As reported by Qian, the above leads to this warning in
> > !CONFIG_NO_HZ_COMMON configs:
> >
> >   kernel/sched/fair.c: In function 'update_blocked_averages':
> >   kernel/sched/fair.c:7750:7: warning: variable 'done' set but not used
> >   [-Wunused-but-set-variable]
> >
> > It wouldn't be wrong to keep cfs_rq_has_blocked() and
> > others_have_blocked() as they are, but since their only current use is
> > to figure out when we can stop calling update_blocked_averages() on
> > fully decayed NOHZ idle CPUs, we can give them a new definition for
> > !CONFIG_NO_HZ_COMMON.
> >
> > Change the definition of cfs_rq_has_blocked() and
> > others_have_blocked() for !CONFIG_NO_HZ_COMMON so that the
> > NOHZ-specific blocks of update_blocked_averages() become no-ops and
> > the 'done' variable gets optimised out.
> >
> > No change in functionality intended.
> >
> > Reported-by: Qian Cai <cai@....pw>
> > Signed-off-by: Valentin Schneider <valentin.schneider@....com>
>
> I'm thinking the below can go on top to further clean up?

For both patches
Acked-by: Vincent Guittot <vincent.guitto@...aro.org>

>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7722,9 +7722,18 @@ static inline bool others_have_blocked(s
>
>         return false;
>  }
> +
> +static inline void update_blocked_load_status(struct rq *rq, bool has_blocked)
> +{
> +       rq->last_blocked_load_update_tick = jiffies;
> +
> +       if (!has_blocked)
> +               rq->has_blocked_load = 0;
> +}
>  #else
>  static inline bool cfs_rq_has_blocked(struct cfs_rq *cfs_rq) { return false; }
>  static inline bool others_have_blocked(struct rq *rq) { return false; }
> +static inline void update_blocked_load_status(struct rq *rq, bool has_blocked) {}
>  #endif
>
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> @@ -7746,18 +7755,6 @@ static inline bool cfs_rq_is_decayed(str
>         return true;
>  }
>
> -#ifdef CONFIG_NO_HZ_COMMON
> -static inline void update_blocked_load_status(struct rq *rq, bool has_blocked)
> -{
> -       rq->last_blocked_load_update_tick = jiffies;
> -
> -       if (!has_blocked)
> -               rq->has_blocked_load = 0;
> -}
> -#else
> -static inline void update_blocked_load_status(struct rq *rq, bool has_blocked) {}
> -#endif
> -
>  static void update_blocked_averages(int cpu)
>  {
>         struct rq *rq = cpu_rq(cpu);
> @@ -7870,11 +7867,7 @@ static inline void update_blocked_averag
>         update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>         update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>         update_irq_load_avg(rq, 0);
> -#ifdef CONFIG_NO_HZ_COMMON
> -       rq->last_blocked_load_update_tick = jiffies;
> -       if (!cfs_rq_has_blocked(cfs_rq) && !others_have_blocked(rq))
> -               rq->has_blocked_load = 0;
> -#endif
> +       update_blocked_load_status(rq, cfs_rq_has_blocked(cfs_rq) || others_have_blocked(rq));
>         rq_unlock_irqrestore(rq, &rf);
>  }
>