Messages in this thread | | | Date | Sat, 26 Jul 2014 21:39:10 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2 0/5] sched: Add on_rq states and remove several double rq locks |
| |
Hi Kirill,
I'll try to read this series later, just one silly question for now.
On 07/26, Kirill Tkhai wrote: > > Patch [2/5] is main in the series. It introduces new state: ONRQ_MIGRATING > and teaches scheduler to understand it (we need a little changes predominantly > in try_to_wake_up()). This will be used in the following way: > > (we are changing task's rq) > > raw_spin_lock(&src_rq->lock); > dequeue_task(src_rq, p, 0); > p->on_rq = ONRQ_MIGRATING; > set_task_cpu(p, dst_cpu); > raw_spin_unlock(&src_rq->lock); > > raw_spin_lock(&dst_rq->lock); > p->on_rq = ONRQ_QUEUED; > enqueue_task(dst_rq, p, 0); > raw_spin_unlock(&dst_rq->lock);
Hmm. And what if the code above doesn't hold p->pi_lock (4/5) and, say, __sched_setscheduler() does fair_sched_class->rt_sched_class transition in between?
ONRQ_MIGRATING helps to avoid the wrong dequeue + enqueue, but I am not sure about check_class_changed().
Say, switched_from_fair() will use dst_rq even if p was never queued on this rq... This only affects the .decay_count logic, perhaps this is fine, I simply do not know what this code does.
What about switched_to_rt() ? we lose the push_rt_task() logic... Hmm, which I can't understand too ;)
And we also lose ENQUEUE_HEAD in this case, but this looks fine.
In short: could you confirm there are no problems here?
Oleg.
| |