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Message-ID: <d4d849e3-ea4b-1f84-b287-513fb7bff415@huawei.com>
Date: Tue, 7 Mar 2023 21:41:25 +0800
From: Zhang Qiao <zhangqiao22@...wei.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
CC: <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
<peterz@...radead.org>, <juri.lelli@...hat.com>,
<dietmar.eggemann@....com>, <rostedt@...dmis.org>,
<bsegall@...gle.com>, <mgorman@...e.de>, <bristot@...hat.com>,
<vschneid@...hat.com>, <rkagan@...zon.de>
Subject: Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated
在 2023/3/7 18:26, Vincent Guittot 写道:
> On Mon, 6 Mar 2023 at 14:53, Vincent Guittot <vincent.guittot@...aro.org> wrote:
>>
>> On Mon, 6 Mar 2023 at 13:57, 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 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>
>>
>> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
>>
>>> ---
>>>
>>> v1 -> v2:
>>> - fix some typos and update comments
>>> - reformat the patch
>>>
>>> ---
>>> kernel/sched/fair.c | 76 ++++++++++++++++++++++++++++++++-------------
>>> 1 file changed, 55 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index 7a1b1f855b96..74c9918ffe76 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -4648,11 +4648,45 @@ 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)
>>> +{
>>> + 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)
>>> {
>>> u64 vruntime = cfs_rq->min_vruntime;
>>> - u64 sleep_time;
>>>
>>> /*
>>> * The 'current' period is already promised to the current tasks,
>>> @@ -4664,23 +4698,8 @@ 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 +4708,7 @@ 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 +7653,23 @@ 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 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 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. Because waking
>>> + * task's vruntime will be added to cfs_rq->min_vruntime when
>>> + * enqueue, we only need to reset the se->vruntime of waking task
>>> + * to a credit here.
>>> + */
>>> + if (entity_is_long_sleep(se))
>
> I completely overlooked that we can't use rq_clock_task here. Need to
> think a bit more on this
Hi,Vincent,
How about using exec_start of the parent sched_entity instant of rq_clock_task()?
If during the waking sched_entity sleep, there are sibling sched_entity running,
than `pse->exec_start` was up to date.
If the cfs_rq was idle, we don't have a problem of possible overflow.
static inline bool vruntime_need_sanitized(struct sched_entity *se)
{
struct sched_entity *pse = parent_entity(se);
u64 diff ;
if (se->exec_start == 0 || !pse)
return false;
diff = pse->exec_start - se->exec_start;
if ((s64)diff > 60LL * NSEC_PER_SEC)
return true;
return false;
}
Thanks.
ZhangQiao.
>
>>> + 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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