Messages in this thread | | | Subject | Re: [RFC][PATCH 08/17] sched: Drop the rq argument to sched_class::select_task_rq() | From | Peter Zijlstra <> | Date | Mon, 03 Jan 2011 12:16:49 +0100 |
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On Wed, 2010-12-29 at 22:31 +0800, Yong Zhang wrote: > On Fri, Dec 24, 2010 at 01:23:46PM +0100, Peter Zijlstra wrote: > > In preparation of calling select_task_rq() without rq->lock held, drop > > the dependency on the rq argument. > > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > > --- > > @@ -3416,27 +3409,22 @@ void sched_exec(void) > > { > > struct task_struct *p = current; > > unsigned long flags; > > - struct rq *rq; > > int dest_cpu; > > > > - rq = task_rq_lock(p, &flags); > > - dest_cpu = p->sched_class->select_task_rq(rq, p, SD_BALANCE_EXEC, 0); > > + raw_spin_lock_irqsave(&p->pi_lock, flags); > > Seems this should go to patch 07/17 ;)
Ah, the reason its here is that this patch removes the rq argument and thus we no longer need rq->lock. So this part relies on the property introduced by patch 7.
> > + dest_cpu = p->sched_class->select_task_rq(p, SD_BALANCE_EXEC, 0); > > if (dest_cpu == smp_processor_id()) > > goto unlock; > > > > - /* > > - * select_task_rq() can race against ->cpus_allowed > > - */ > > - if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed) && > > - likely(cpu_active(dest_cpu)) && migrate_task(p, rq)) { > > + if (likely(cpu_active(dest_cpu)) && need_migrate_task(p)) { > > If we drop rq_lock, need_migrate_task() maybe return true but > p is already running on other cpu. Thus we do a wrong migration > call.
Yeah, too bad.. ;-) exec load balancing is more an optimistic thing anyway, if it got rebalanced under out feet we don't care.
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