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SubjectRe: [PATCH v2 2/2] sched/fair: Advance global expiration when period timer is restarted
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Xunlei Pang <xlpang@linux.alibaba.com> writes:

> When period gets restarted after some idle time, start_cfs_bandwidth()
> doesn't update the expiration information, expire_cfs_rq_runtime() will
> see cfs_rq->runtime_expires smaller than rq clock and go to the clock
> drift logic, wasting needless cpu cycles on the scheduler hot path.
>
> Update the global expiration in start_cfs_bandwidth() to avoid frequent
> expire_cfs_rq_runtime() calls once a new period begins.
>
> Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
Reviewed-By: Ben Segall <bsegall@google.com>


> ---
> kernel/sched/fair.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e6bb68d52962..f167aca066cc 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5204,13 +5204,18 @@ 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) {
> - 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);
> - }
> + if (cfs_b->period_active)
> + return;
> +
> + cfs_b->period_active = 1;
> + overrun = hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
> + cfs_b->runtime_expires += (overrun + 1) * ktime_to_ns(cfs_b->period);
> + cfs_b->expires_seq++;
> + hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
> }
>
> static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)

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