linux-kernel - Re: [PATCH -next v2] sched/fair: fix -Wunused-but-set-variable warnings

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Date:   Tue, 10 Sep 2019 16:58:01 -0400
From:   Qian Cai <cai@....pw>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, bsegall@...gle.com, chiluk+linux@...eed.com,
        pauld@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v2] sched/fair: fix -Wunused-but-set-variable
 warnings

On Tue, 2019-09-03 at 16:15 +0200, Peter Zijlstra wrote:
> On Tue, Sep 03, 2019 at 09:03:26AM -0400, Qian Cai wrote:
> > Ingo or Peter, please take a look at this trivial patch. Still see the warning
> > in linux-next every day.
> > 
> > On Tue, 2019-08-20 at 14:40 -0400, Qian Cai wrote:
> > > The linux-next commit "sched/fair: Fix low cpu usage with high
> > > throttling by removing expiration of cpu-local slices" [1] 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.
> > > 
> > > [1] https://lore.kernel.org/lkml/1558121424-2914-1-git-send-email-chiluk+linux
> > > @indeed.com/
> > > 
> > > Signed-off-by: Qian Cai <cai@....pw>
> 
> Rewrote the Changelog like so:

Looks good. I suppose it still need Ingo to pick it up, as today's tip/auto-
latest still show those warnings.

> 
> ---
> Subject: sched/fair: Fix -Wunused-but-set-variable warnings
> From: Qian Cai <cai@....pw>
> Date: Tue, 20 Aug 2019 14:40:55 -0400
> 
> 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")
> Signed-off-by: Qian Cai <cai@....pw>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Ben Segall <bsegall@...gle.com>
> Reviewed-by: Dave Chiluk <chiluk+linux@...eed.com>
> Cc: mingo@...hat.com
> Cc: pauld@...hat.com
> Link: https://lkml.kernel.org/r/1566326455-8038-1-git-send-email-cai@lca.pw
> ---
>  kernel/sched/fair.c |   19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
> 
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4386,21 +4386,16 @@ static inline u64 sched_cfs_bandwidth_sl
>  }
>  
>  /*
> - * 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)
> @@ -5021,15 +5016,13 @@ static void init_cfs_rq_runtime(struct c
>  
>  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);
>  }
>