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Message-ID: <xm26jznh2s25.fsf@google.com>
Date: Tue, 06 Feb 2024 13:36:50 -0800
From: Benjamin Segall <bsegall@...gle.com>
To: Valentin Schneider <vschneid@...hat.com>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Peter
Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann
<dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Mel
Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira
<bristot@...hat.com>, Phil Auld <pauld@...hat.com>, Clark Williams
<williams@...hat.com>, Tomas Glozar <tglozar@...hat.com>
Subject: Re: [RFC PATCH v2 3/5] sched/fair: Delete cfs_rq_throttled_loose(),
use cfs_rq->throttle_pending instead
Valentin Schneider <vschneid@...hat.com> writes:
> cfs_rq_throttled_loose() does not check if there is runtime remaining in
> the cfs_b, and thus relies on check_cfs_rq_runtime() being ran previously
> for that to be checked.
>
> Cache the throttle attempt in throttle_cfs_rq and reuse that where
> needed.
The general idea of throttle_pending rather than constantly checking
runtime_remaining seems reasonable...
>
> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
> ---
> kernel/sched/fair.c | 44 ++++++++++----------------------------------
> 1 file changed, 10 insertions(+), 34 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 96504be6ee14a..60778afbff207 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5462,7 +5462,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
> * 5) do not run the "skip" process, if something else is available
> */
> static struct sched_entity *
> -pick_next_entity(struct cfs_rq *cfs_rq, bool throttled)
> +pick_next_entity(struct cfs_rq *cfs_rq)
> {
> #ifdef CONFIG_CFS_BANDWIDTH
> /*
> @@ -5473,7 +5473,7 @@ pick_next_entity(struct cfs_rq *cfs_rq, bool throttled)
> * throttle_cfs_rq.
> */
> WARN_ON_ONCE(list_empty(&cfs_rq->kernel_children));
> - if (throttled && !list_empty(&cfs_rq->kernel_children)) {
> + if (cfs_rq->throttle_pending && !list_empty(&cfs_rq->kernel_children)) {
.. but we still need to know here if any of our parents are throttled
as well, ie a "throttled_pending_count", or to keep the "throttled"
parameter tracking in pnt_fair. (ie just replace the implementation of
cfs_rq_throttled_loose).
> /*
> * TODO: you'd want to factor out pick_eevdf to just take
> * tasks_timeline, and replace this list with a second rbtree
> @@ -5791,8 +5791,12 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
> * We don't actually throttle, though account() will have made sure to
> * resched us so that we pick into a kernel task.
> */
> - if (cfs_rq->h_kernel_running)
> + if (cfs_rq->h_kernel_running) {
> + cfs_rq->throttle_pending = true;
> return false;
> + }
> +
> + cfs_rq->throttle_pending = false;
We also need to clear throttle_pending if quota refills and our
runtime_remaining goes positive. (And do the appropriate h_* accounting in
patch 4/5)
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