linux-kernel - Re: [PATCH] sched/fair: fix -Wunused-but-set-variable warnings

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Date:   Wed, 18 Sep 2019 15:11:41 -0500
From:   Dave Chiluk <chiluk+linux@...eed.com>
To:     Qian Cai <cai@....pw>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, Ben Segall <bsegall@...gle.com>,
        mgorman@...e.de, Phil Auld <pauld@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: fix -Wunused-but-set-variable warnings

de53fd7aedb1 has just been merged into Linus' mainline tree for
eventual inclusion in 5.4.  This should be pushed into there, and not
wait till 5.5.

Both I and Ben Segall have already +1'd this in previous threads.

Sorry for introducing the warnings.

Dave.

On Wed, Sep 18, 2019 at 2:02 PM Qian Cai <cai@....pw> wrote:
>
> The commit de53fd7aedb1 ("sched/fair: Fix low cpu usage with high
> throttling by removing expiration of cpu-local slices") introduced a few
> compilation warnings:
>
>   kernel/sched/fair.c: In function '__refill_cfs_bandwidth_runtime':
>   kernel/sched/fair.c:4365:6: warning: variable 'now' set but not used
>     [-Wunused-but-set-variable]
>   kernel/sched/fair.c: In function 'start_cfs_bandwidth':
>   kernel/sched/fair.c:4992:6: warning: variable 'overrun' set but not
>     used [-Wunused-but-set-variable]
>
> Also, __refill_cfs_bandwidth_runtime() does no longer update the
> expiration time, so fix the comments accordingly.
>
> Fixes: de53fd7aedb1 ("sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices")
> Reviewed-by: Ben Segall <bsegall@...gle.com>
> Reviewed-by: Dave Chiluk <chiluk+linux@...eed.com>
> Signed-off-by: Qian Cai <cai@....pw>
> ---
>
> Resend it since the offensive commit is now in the mainline.
>
>  kernel/sched/fair.c | 19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d4bbf68c3161..b4fb016e3557 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4354,21 +4354,16 @@ static inline u64 sched_cfs_bandwidth_slice(void)
>  }
>
>  /*
> - * Replenish runtime according to assigned quota and update expiration time.
> - * We use sched_clock_cpu directly instead of rq->clock to avoid adding
> - * additional synchronization around rq->lock.
> + * Replenish runtime according to assigned quota. We use sched_clock_cpu
> + * directly instead of rq->clock to avoid adding additional synchronization
> + * around rq->lock.
>   *
>   * requires cfs_b->lock
>   */
>  void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
>  {
> -       u64 now;
> -
> -       if (cfs_b->quota == RUNTIME_INF)
> -               return;
> -
> -       now = sched_clock_cpu(smp_processor_id());
> -       cfs_b->runtime = cfs_b->quota;
> +       if (cfs_b->quota != RUNTIME_INF)
> +               cfs_b->runtime = cfs_b->quota;
>  }
>
>  static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
> @@ -4994,15 +4989,13 @@ static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
>
>  void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
>  {
> -       u64 overrun;
> -
>         lockdep_assert_held(&cfs_b->lock);
>
>         if (cfs_b->period_active)
>                 return;
>
>         cfs_b->period_active = 1;
> -       overrun = hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
> +       hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
>         hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
>  }
>
> --
> 1.8.3.1
>