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Date: Mon, 6 Mar 2023 12:12:29 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Zhang Qiao <zhangqiao22@...wei.com>
Cc: lkml <linux-kernel@...r.kernel.org>,
Valentin Schneider <vschneid@...hat.com>,
Ben Segall <bsegall@...gle.com>,
Waiman Long <longman@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Mel Gorman <mgorman@...e.de>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH] sched/fair: sanitize vruntime of entity being migrated
On Sat, 4 Mar 2023 at 09:29, Zhang Qiao <zhangqiao22@...wei.com> wrote:
>
> Commit 829c1651e9c4 ("sched/fair: sanitize vruntime of
> entity being placed") fix an overflowing bug, but ignore
> a case that se->exec_start is reset after a migration.
>
> For fix this case, we reset the vruntime of a loog sleep
> task in migrate_task_rq_fair().
some typo:
"For fixing this case, we reset the vruntime of a long sleeping task
in migrate_task_rq_fair()."
>
> Fixes: 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed")
> Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
Your patch doesn't apply. It seems to be malformed
> ---
> kernel/sched/fair.c | 73 ++++++++++++++++++++++++++++++++-------------
> 1 file changed, 53 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ff4dbbae3b10..6697462baf0f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4648,6 +4648,41 @@ static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
> #endif
> }
> +static inline bool entity_is_long_sleep(struct sched_entity *se)
This extra space at the beg of the line above looks strange
> +{
> + struct cfs_rq *cfs_rq;
> + u64 sleep_time;
> +
> + if (se->exec_start == 0)
> + return false;
> +
> + cfs_rq = cfs_rq_of(se);
> + sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start;
> + if ((s64)sleep_time > 60LL * NSEC_PER_SEC)
> + return true;
> +
> + return false;
> +}
> +
> +static inline u64 sched_sleeper_credit(struct sched_entity *se)
> +{
> + unsigned long thresh;
> +
> + if (se_is_idle(se))
> + thresh = sysctl_sched_min_granularity;
> + else
> + thresh = sysctl_sched_latency;
> +
> + /*
> + * Halve their sleep time's effect, to allow
> + * for a gentler effect of sleepers:
> + */
> + if (sched_feat(GENTLE_FAIR_SLEEPERS))
> + thresh >>= 1;
> +
> + return thresh;
> +}
> +
> static void
> place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
> {
> @@ -4664,23 +4699,8 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
> vruntime += sched_vslice(cfs_rq, se);
> /* sleeps up to a single latency don't count. */
> - if (!initial) {
> - unsigned long thresh;
> -
> - if (se_is_idle(se))
> - thresh = sysctl_sched_min_granularity;
> - else
> - thresh = sysctl_sched_latency;
> -
> - /*
> - * Halve their sleep time's effect, to allow
> - * for a gentler effect of sleepers:
> - */
> - if (sched_feat(GENTLE_FAIR_SLEEPERS))
> - thresh >>= 1;
> -
> - vruntime -= thresh;
> - }
> + if (!initial)
> + vruntime -= sched_sleeper_credit(se);
> /*
> * Pull vruntime of the entity being placed to the base level of
> @@ -4689,8 +4709,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
> * the base as it may be too far off and the comparison may get
> * inversed due to s64 overflow.
> */
> - sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start;
> - if ((s64)sleep_time > 60LL * NSEC_PER_SEC)
> + if (entity_is_long_sleep(se))
> se->vruntime = vruntime;
> else
> se->vruntime = max_vruntime(se->vruntime, vruntime);
> @@ -7635,7 +7654,21 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu)
> if (READ_ONCE(p->__state) == TASK_WAKING) {
> struct cfs_rq *cfs_rq = cfs_rq_of(se);
> - se->vruntime -= u64_u32_load(cfs_rq->min_vruntime);
> + /*
> + * We determine a task whether sleep for long by checking se->exec_start,
> + * and if it is, sanitize its vruntime at place_entity(). However, after
> + * a migration, this detection method fails due to se->exec_start is reset.
some typo
"We determine whether a task sleeps for long by checking
se->exec_start, and if it is, we sanitize its vruntime at
place_entity(). However, after a migration, this detection method
fails due to se->exec_start being reset."
> + *
> + * For fix this case, we add the same check at here. For a task which has
> + * slept for long, its vruntime should be reset cfs_rq->min_vruntime and get
> + * a sleep credit. Because waking task's vruntime will be added cfs_rq->min_vruntime
For fixing this case, we add the same check here. For a task which has
slept for a long time, its vruntime should be reset to
cfs_rq->min_vruntime with a sleep credit.
Beside the typo and malformed patch, the proposed fix looks good to me
> + * when enqueue, so we only need resetting the se->vruntime of waking task
> + * to a credit at here.
> + */
> + if (entity_is_long_sleep(se))
> + se->vruntime = -sched_sleeper_credit(se);
> + else
> + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime);
> }
> if (!task_on_rq_migrating(p)) {
> --
> 2.17.1
>
> .
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