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sched/fair: Make SCHED_IDLE entity be preempted in strict hierarchy

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Consider the following cgroup:

                       root
                        |
             ------------------------
             |                      |
       normal_cgroup            idle_cgroup
             |                      |
   SCHED_IDLE task_A           SCHED_NORMAL task_B

According to the cgroup hierarchy, A should preempt B. But current
check_preempt_wakeup_fair() treats cgroup se and task separately, so B
will preempt A unexpectedly.
Unify the wakeup logic by {c,p}se_is_idle only. This makes SCHED_IDLE of
a task a relative policy that is effective only within its own cgroup,
similar to the behavior of NICE.

Also fix se_is_idle() definition when !CONFIG_FAIR_GROUP_SCHED.

Fixes: 304000390f ("sched: Cgroup SCHED_IDLE support")
Signed-off-by: Tianchen Ding <dtcccc@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Don <joshdon@google.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20240626023505.1332596-1-dtcccc@linux.alibaba.com
This commit is contained in:
Tianchen Ding 2024-06-26 10:35:05 +08:00 committed by Peter Zijlstra
parent a58501fb83
commit faa42d2941
1 changed files with 9 additions and 13 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

22
kernel/sched/fair.c
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@ -511,7 +511,7 @@ static int cfs_rq_is_idle(struct cfs_rq *cfs_rq)
static int se_is_idle(struct sched_entity *se)
{
return 0;
return task_has_idle_policy(task_of(se));
}
#endif /* CONFIG_FAIR_GROUP_SCHED */
@ -8381,16 +8381,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
if (test_tsk_need_resched(curr))
return;
/* Idle tasks are by definition preempted by non-idle tasks. */
if (unlikely(task_has_idle_policy(curr)) &&
likely(!task_has_idle_policy(p)))
goto preempt;
/*
* Batch and idle tasks do not preempt non-idle tasks (their preemption
* is driven by the tick):
*/
if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
if (!sched_feat(WAKEUP_PREEMPTION))
return;
find_matching_se(&se, &pse);
@ -8400,7 +8391,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
pse_is_idle = se_is_idle(pse);
/*
* Preempt an idle group in favor of a non-idle group (and don't preempt
* Preempt an idle entity in favor of a non-idle entity (and don't preempt
* in the inverse case).
*/
if (cse_is_idle && !pse_is_idle)
@ -8408,9 +8399,14 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
if (cse_is_idle != pse_is_idle)
return;
/*
* BATCH and IDLE tasks do not preempt others.
*/
if (unlikely(p->policy != SCHED_NORMAL))
return;
cfs_rq = cfs_rq_of(se);
update_curr(cfs_rq);
/*
* XXX pick_eevdf(cfs_rq) != se ?
*/