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SubjectRe: [PATCH 1/2] sched/fair: skip newidle update stats
On Fri, 12 Nov 2021 at 15:55, Peter Zijlstra <peterz@infradead.org> wrote:
>
>
> Subject: sched/fair: Reflow newidle_balance()
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Fri Nov 12 15:46:08 CET 2021
>
> The control flow in newidle_balance() is a little convoluted, attempt
> simplification.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/sched/fair.c | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10858,10 +10858,10 @@ static inline void nohz_newidle_balance(
> static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
> {
> unsigned long next_balance = jiffies + HZ;
> + int pulled_task = 0, timeout = 0;
> int this_cpu = this_rq->cpu;
> u64 t0, t1, curr_cost = 0;
> struct sched_domain *sd;
> - int pulled_task = 0, early_stop = 0;
>
> update_misfit_status(NULL, this_rq);
>
> @@ -10889,17 +10889,9 @@ static int newidle_balance(struct rq *th
> if (!READ_ONCE(this_rq->rd->overload) ||
> (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
>
> - if (sd) {
> + if (sd)
> update_next_balance(sd, &next_balance);
>
> - /*
> - * We skip new idle LB because there is not enough
> - * time before next wake up. Make sure that we will
> - * not kick NOHZ_NEWILB_KICK
> - */
> - early_stop = 1;
> - }
> -
> goto out;
> }
>
> @@ -10922,7 +10914,7 @@ static int newidle_balance(struct rq *th
> update_next_balance(sd, &next_balance);
>
> if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) {
> - early_stop = 1;
> + timeout = 1;
> break;
> }
>
> @@ -10967,6 +10959,11 @@ static int newidle_balance(struct rq *th
> if (this_rq->nr_running != this_rq->cfs.h_nr_running)
> pulled_task = -1;
>
> + if (pulled_task || timeout)
> + goto out;
> +
> + nohz_newidle_balance(this_rq);

maybe

if (!pulled_task && !timeout)
nohz_newidle_balance(this_rq);

> +
> out:
> /* Move the next balance forward */
> if (time_after(this_rq->next_balance, next_balance))
> @@ -10974,8 +10971,6 @@ static int newidle_balance(struct rq *th
>
> if (pulled_task)
> this_rq->idle_stamp = 0;
> - else if (!early_stop)
> - nohz_newidle_balance(this_rq);
>
> return pulled_task;
> }

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