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Date: Mon, 6 Mar 2023 20:26:15 +0800
From: Zhang Qiao <zhangqiao22@...wei.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
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
在 2023/3/6 19:12, Vincent Guittot 写道:
> 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
HI, Vincent,
Thank you for your correction.
>
>> + * 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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