Messages in this thread | | | Date | Tue, 22 Aug 2023 17:20:20 +0200 | Subject | Re: [PATCH v5 16/19] sched: Fix proxy/current (push,pull)ability | From | Dietmar Eggemann <> |
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On 19/08/2023 08:08, John Stultz wrote: > From: Valentin Schneider <valentin.schneider@arm.com>
[...]
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index bee7082b294f..e8065fc5c894 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6656,6 +6656,21 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf) > raw_spin_unlock(&mutex->wait_lock); > return ret; > } > + > +static inline void proxy_tag_curr(struct rq *rq, struct task_struct *next) > +{ > + /* > + * pick_next_task() calls set_next_task() on the selected task > + * at some point, which ensures it is not push/pullable. > + * However, the selected task *and* the ,mutex owner form an > + * atomic pair wrt push/pull. > + * > + * Make sure owner is not pushable. Unfortunately we can only > + * deal with that by means of a dequeue/enqueue cycle. :-/ > + */ > + dequeue_task(rq, next, DEQUEUE_NOCLOCK | DEQUEUE_SAVE); > + enqueue_task(rq, next, ENQUEUE_NOCLOCK | ENQUEUE_RESTORE); > +} > #else /* PROXY_EXEC */ > static struct task_struct * > proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf) > @@ -6663,6 +6678,8 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf) > BUG(); // This should never be called in the !PROXY case > return next; > } > + > +static inline void proxy_tag_curr(struct rq *rq, struct task_struct *next) { } > #endif /* PROXY_EXEC */ > > /* > @@ -6711,6 +6728,7 @@ static void __sched notrace __schedule(unsigned int sched_mode) > unsigned long prev_state; > struct rq_flags rf; > struct rq *rq; > + bool proxied; > int cpu; > > cpu = smp_processor_id(); > @@ -6760,6 +6778,7 @@ static void __sched notrace __schedule(unsigned int sched_mode) > switch_count = &prev->nvcsw; > } > > + proxied = (rq_selected(rq) != prev);
Looks like proxied isn't used here. (*)
> pick_again: > next = pick_next_task(rq, rq_selected(rq), &rf); > rq_set_selected(rq, next); > @@ -6786,6 +6805,10 @@ static void __sched notrace __schedule(unsigned int sched_mode) > * changes to task_struct made by pick_next_task(). > */ > RCU_INIT_POINTER(rq->curr, next); > + > + if (unlikely(!task_current_selected(rq, next))) > + proxy_tag_curr(rq, next); > + > /* > * The membarrier system call requires each architecture > * to have a full memory barrier after updating > @@ -6810,6 +6833,10 @@ static void __sched notrace __schedule(unsigned int sched_mode) > /* Also unlocks the rq: */ > rq = context_switch(rq, prev, next, &rf); > } else { > + /* In case next was already curr but just got blocked_donor*/ > + if (unlikely(!task_current_selected(rq, next))) > + proxy_tag_curr(rq, next);
(*) v4 had:
+ /* In case next was already curr but just got blocked_donor*/ + if (unlikely(!proxied && next->blocked_donor))
> + > rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP); > > rq_unpin_lock(rq, &rf);
I miss changes in enqueue_task_rt() and put_prev_task_rt() related to 'affinity of blocked tasks doesn't matter' from v4.
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