Messages in this thread Patch in this message | | | Date | Mon, 20 Feb 2023 18:38:00 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH] sched/fair: Interleave cfs bandwidth timers for improved single thread performance at low utilization |
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On Tue, Feb 14, 2023 at 08:54:09PM +0530, shrikanth hegde wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index ff4dbbae3b10..7b69c329e05d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5939,14 +5939,25 @@ static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) > > void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b) > { > - lockdep_assert_held(&cfs_b->lock); > + struct hrtimer *period_timer = &cfs_b->period_timer; > + s64 incr = ktime_to_ns(cfs_b->period) / 10; > + ktime_t delta; > + u64 orun = 1; > > + lockdep_assert_held(&cfs_b->lock); > if (cfs_b->period_active) > return; > > cfs_b->period_active = 1; > - hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period); > - hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED); > + delta = ktime_sub(period_timer->base->get_time(), > + hrtimer_get_expires(period_timer)); > + if (unlikely(delta >= cfs_b->period)) { > + orun = ktime_divns(delta, incr); > + hrtimer_add_expires_ns(period_timer, incr * orun); > + } > + > + hrtimer_forward_now(period_timer, cfs_b->period); > + hrtimer_start_expires(period_timer, HRTIMER_MODE_ABS_PINNED); > }
What kind of mad hackery is this? Why can't you do the sane thing and initialize the timer at !0 in init_cfs_bandwidth(), then any of the forwards will stay in period -- as they should.
Please, go re-read Thomas's email.
*completely* untested...
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7c46485d65d7..4d6ea76096dc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5915,6 +5915,7 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq); hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED); + cfs_b->period_timer.node.expires = get_random_u32_below(cfs_b->period); cfs_b->period_timer.function = sched_cfs_period_timer; hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); cfs_b->slack_timer.function = sched_cfs_slack_timer;
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