On Fri, Mar 15, 2019 at 11:11:50AM +0100 Peter Zijlstra wrote: > On Wed, Mar 13, 2019 at 11:08:26AM -0400, Phil Auld wrote:
... > Computers _suck_ at /100. And since you're free to pick the constant, > pick a power of two, computers love those. > > > + > > + if (new_period > max_cfs_quota_period) > > + new_period = max_cfs_quota_period; > > + > > + cfs_b->period = ns_to_ktime(new_period); > > + cfs_b->quota += (cfs_b->quota * ((new_period - > > old_period) * 100)/old_period)/100; > > srsly!? Again, you can pick the constant to be anything, and you pick > such a horrid number?! > In my defense here, all the fair.c imbalance pct code also uses 100 :) > > + pr_warn_ratelimited( > > + "cfs_period_timer[cpu%d]: period too short, > > scaling up (new cfs_period_us %lld, cfs_quota_us = %lld)\n", > > + smp_processor_id(), > > cfs_b->period/NSEC_PER_USEC, cfs_b->quota/NSEC_PER_USEC); > > period was ktime_t, remember... Indeed. Worked but was incorrect. > > Would not something simpler like the below also work? With my version: [ 4246.030004] cfs_period_timer[cpu16]: period too short, scaling up (new cfs_period_us 5276, cfs_quota_us = 303973) [ 4246.346978] cfs_period_timer[cpu16]: period too short, scaling up (new cfs_period_us 17474, cfs_quota_us = 1006569) (most of the time it's only one message. Sometimes it does a smaller increase once first like this) with the below: [ 117.235804] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 2492, cfs_quota_us = 143554) [ 117.346807] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 2862, cfs_quota_us = 164863) [ 117.470569] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 3286, cfs_quota_us = 189335) [ 117.574883] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 3774, cfs_quota_us = 217439) [ 117.652907] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 4335, cfs_quota_us = 249716) [ 118.090535] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 4978, cfs_quota_us = 286783) [ 122.098009] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 5717, cfs_quota_us = 329352) [ 126.255209] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 6566, cfs_quota_us = 378240) [ 126.358060] cfs_period_timer[cpu2]: period too short, scaling up (new cfs_period_us 7540, cfs_quota_us = 434385) [ 126.538358] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 8660, cfs_quota_us = 498865) [ 126.614304] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 9945, cfs_quota_us = 572915) [ 126.817085] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 11422, cfs_quota_us = 657957) [ 127.352038] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 13117, cfs_quota_us = 755623) [ 127.598043] cfs_period_timer[cpu9]: period too short, scaling up (new cfs_period_us 15064, cfs_quota_us = 867785) Plus on repeats I see an occasional [ 152.803384] sched_cfs_period_timer: 9 callbacks suppressed I'll rework the maths in the averaged version and post v2 if that makes sense. It may have the extra timer fetch, although maybe I could rework it so that it used the nsstart time the first time and did not need to do it twice in a row. I had originally reverted the hrtimer_forward_now() to hrtimer_forward() but put that back. Thanks for looking at it. Also, fwiw, this was reported earlier by Anton Blanchard in https://lkml.org/lkml/2018/12/3/1047 Cheers, Phil > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ea74d43924b2..b71557be6b42 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4885,6 +4885,8 @@ static enum hrtimer_restart > sched_cfs_slack_timer(struct hrtimer *timer) > return HRTIMER_NORESTART; > } > > +extern const u64 max_cfs_quota_period; > + > static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > { > struct cfs_bandwidth *cfs_b = > @@ -4892,6 +4894,7 @@ static enum hrtimer_restart > sched_cfs_period_timer(struct hrtimer *timer) > unsigned long flags; > int overrun; > int idle = 0; > + int count = 0; > > raw_spin_lock_irqsave(&cfs_b->lock, flags); > for (;;) { > @@ -4899,6 +4902,28 @@ static enum hrtimer_restart > sched_cfs_period_timer(struct hrtimer *timer) > if (!overrun) > break; > > + if (++count > 3) { > + u64 new, old = ktime_to_ns(cfs_b->period); > + > + new = (old * 147) / 128; /* ~115% */ > + new = min(new, max_cfs_quota_period); > + > + cfs_b->period = ns_to_ktime(new); > + > + /* since max is 1s, this is limited to 1e9^2, which > fits in u64 */ > + cfs_b->quota *= new; > + cfs_b->quota /= old; > + > + pr_warn_ratelimited( > + "cfs_period_timer[cpu%d]: period too short, scaling up (new > cfs_period_us %lld, cfs_quota_us = %lld)\n", > + smp_processor_id(), > + new/NSEC_PER_USEC, > + cfs_b->quota/NSEC_PER_USEC); > + > + /* reset count so we don't come right back in here */ > + count = 0; > + } > + > idle = do_sched_cfs_period_timer(cfs_b, overrun, flags); > } > if (idle) --
