Messages in this thread | | | Date | Mon, 24 Oct 2022 12:13:15 +0200 | Subject | Re: [RFC PATCH 07/11] sched: Add proxy execution | From | Dietmar Eggemann <> |
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On 03/10/2022 23:44, Connor O'Brien wrote: > From: Peter Zijlstra <peterz@infradead.org>
[...]
> + * Returns the task that is going to be used as execution context (the one > + * that is actually going to be put to run on cpu_of(rq)). > + */ > +static struct task_struct * > +proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf) > +{
[...]
> +migrate_task:
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> + /* > + * Since we're going to drop @rq, we have to put(@next) first, > + * otherwise we have a reference that no longer belongs to us. Use > + * @fake_task to fill the void and make the next pick_next_task() ^^^^^^^^^^
There was a `static struct task_struct fake_task` in https://lkml.kernel.org/r/20181009092434.26221-6-juri.lelli@redhat.com but now IMHO we use `rq->idle` <-- (1)
> + * invocation happy. > + * > + * XXX double, triple think about this. > + * XXX put doesn't work with ON_RQ_MIGRATE > + * > + * CPU0 CPU1 > + * > + * B mutex_lock(X) > + * > + * A mutex_lock(X) <- B > + * A __schedule() > + * A pick->A > + * A proxy->B > + * A migrate A to CPU1 > + * B mutex_unlock(X) -> A > + * B __schedule() > + * B pick->A > + * B switch_to (A) > + * A ... does stuff > + * A ... is still running here > + * > + * * BOOM * > + */ > + put_prev_task(rq, next); > + if (curr_in_chain) { > + rq->proxy = rq->idle; > + set_tsk_need_resched(rq->idle); > + /* > + * XXX [juril] don't we still need to migrate @next to > + * @owner's CPU? > + */ > + return rq->idle; > + }
--> (1)
> + rq->proxy = rq->idle; > + > + for (; p; p = p->blocked_proxy) { > + int wake_cpu = p->wake_cpu; > + > + WARN_ON(p == rq->curr); > + > + deactivate_task(rq, p, 0); > + set_task_cpu(p, that_cpu); > + /* > + * We can abuse blocked_entry to migrate the thing, because @p is > + * still on the rq. > + */ > + list_add(&p->blocked_entry, &migrate_list); > + > + /* > + * Preserve p->wake_cpu, such that we can tell where it > + * used to run later. > + */ > + p->wake_cpu = wake_cpu; > + } > + > + rq_unpin_lock(rq, rf); > + raw_spin_rq_unlock(rq);
Don't we run into rq_pin_lock()'s:
SCHED_WARN_ON(rq->balance_callback && rq->balance_callback != &balance_push_callback)
by releasing rq lock between queue_balance_callback(, push_rt/dl_tasks) and __balance_callbacks()?
[...]
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