Messages in this thread | | | Date | Wed, 21 Aug 2013 13:49:44 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock |
| |
On 08/21, Frederic Weisbecker wrote: > > On Tue, Aug 20, 2013 at 06:33:12PM +0200, Oleg Nesterov wrote: > > > > --- x/kernel/sched/core.c > > +++ x/kernel/sched/core.c > > @@ -2435,6 +2435,9 @@ need_resched: > > rq->curr = next; > > ++*switch_count; > > > > + if (unlikely(prev->in_iowait)) > > + rq->nr_iowait++; > > + > > context_switch(rq, prev, next); /* unlocks the rq */ > > /* > > * The context switch have flipped the stack from under us > > @@ -2442,6 +2445,12 @@ need_resched: > > * this task called schedule() in the past. prev == current > > * is still correct, but it can be moved to another cpu/rq. > > */ > > + if (unlikely(prev->in_iowait)) { > > + raw_spin_lock_irq(&rq->lock); > > + rq->nr_iowait--; > > + raw_spin_unlock_irq(&rq->lock); > > + } > > + > > It seems that with this solution rq->nr_iowait is only ever modified locally. > Can't we just disable irqs for rq->nr_iowait-- ?
Not really. rq holds the old value, which was used when this task called context_switch() in the past.
IOW, if a task T does io_schedule() on CPU_0, then cpu_of(rq) is still 0 after context_switch(), even if T runs on another cpu.
> Also if this is only updated locally,
Unfortunately, I don't see how we can do this.
Oleg.
| |