Messages in this thread | | | Date | Fri, 23 Aug 2019 14:03:42 -0400 | From | Phil Auld <> | Subject | Re: [PATCH -next v2] sched/fair: fix -Wunused-but-set-variable warnings |
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On Fri, Aug 23, 2019 at 10:28:02AM -0700 bsegall@google.com wrote: > Dave Chiluk <chiluk+linux@indeed.com> writes: > > > On Wed, Aug 21, 2019 at 12:36 PM <bsegall@google.com> wrote: > >> > >> Qian Cai <cai@lca.pw> writes: > >> > >> > 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@lca.pw> > >> > >> Reviewed-by: Ben Segall <bsegall@google.com> > >> > >> > --- > >> > > >> > v2: Keep hrtimer_forward_now() in start_cfs_bandwidth() per Ben. > >> > > >> > 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 84959d3285d1..06782491691f 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) > >> > @@ -4989,15 +4984,13 @@ 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); > >> > } > > > > Looks good. > > Reviewed-by: Dave Chiluk <chiluk+linux@indeed.com> > > > > Sorry for the slow response, I was on vacation. > > > > @Ben do you think it would be useful to still capture overrun, and > > WARN on any overruns? We wouldn't expect overruns, but their > > existence would indicate an over-loaded node or too short of a > > cfs_period. Additionally, it would be interesting to see if we could > > capture the offset between when the bandwidth was refilled, and when > > the timer was supposed to fire. I've always done all my calculations > > assuming that the timer fires and is handled exceedingly close to the > > time it was supposed to fire. Although, if the node is running that > > overloaded you probably have many more problems than worrying about > > timer warnings. > > That "overrun" there is not really an overrun - it's the number of > complete periods the timer has been inactive for. It was used so that a > given tg's period timer would keep the same > phase/offset/whatever-you-call-it, even if it goes idle for a while, > rather than having the next period start N ms after a task wakes up. > > Also, poor choices by userspace is not generally something the kernel > generally WARNs on, as I understand it.
I don't think it matters in the start_cfs_bandwidth case, anyway. We do effectively check in sched_cfs_period_timer.
Cleanup looks okay to me as well.
Cheers, Phil
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