On Wed, Aug 15, 2018 at 05:47:57PM +0800, jianchao.wang wrote:
>
>
> On 08/15/2018 04:28 PM, Ming Lei wrote:
> > On Wed, Aug 15, 2018 at 02:39:05PM +0800, jianchao.wang wrote:
> >> Hi Ming
> >>
> >> On 08/11/2018 03:12 PM, Ming Lei wrote:
> >>> @@ -3786,6 +3800,10 @@ int blk_pre_runtime_suspend(struct request_queue *q)
> >>> q->rpm_status = RPM_SUSPENDING;
> >>> }
> >>> spin_unlock_irq(q->queue_lock);
> >>> +
> >>> + if (!ret)
> >>> + blk_freeze_queue_lock(q);
> >>> +
> >>> return ret;
> >>
> >> Requests seem to be able enter the request_queue while the rpm_status is RPM_SUSPENDING
> >> and miss the rpm_resume.
> >
> > Any requests which enters queue during RPM_SUSPENDING will be drained by
> > blk_freeze_queue_lock().
> >
> >>
> >> Even though blk_freeze_queue_lock will drain them before the real suspend start, but looks
> >> like we should stop the suspend at the moment.
> >
> > Good point, even though it doesn't affect the correctness of this runtime PM
> > implementation.
> >
> > We may improve this situation by the following way, what do you think of
> > it?
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index f42197c9f7af..84e1e6c7db87 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -3803,10 +3803,13 @@ int blk_pre_runtime_suspend(struct request_queue *q)
> > {
> > int ret = 0;
> > bool busy = true;
> > + unsigned long last_busy;
> >
> > if (!q->dev)
> > return ret;
> >
> > + last_busy = READ_ONCE(dev->power.last_busy);
> > +
> > if (q->mq_ops)
> > busy = blk_mq_pm_queue_busy(q);
> >
> > @@ -3823,6 +3826,13 @@ int blk_pre_runtime_suspend(struct request_queue *q)
> > if (!ret)
> > blk_freeze_queue_lock(q);
> >
> > + /*
> > + * Any new IO during this window will prevent the current suspend
> > + * from going on
> > + */
> > + if (unlikely(last_busy != READ_ONCE(dev->power.last_busy)))
> > + ret = -EBUSY;
> > +
> > return ret;
> > }
> > EXPORT_SYMBOL(blk_pre_runtime_suspend);
> >
>
> Wow, this is great method !
> Maybe we should add checking as following:
>
>
> + last_busy = READ_ONCE(dev->power.last_busy);
> + if (last_busy == jiffies)
> + return -EBUSY
We may do that, but seems not necessary given the .runtime_suspend()
(scsi_runtime_suspend) is just called when the timer is expired.
As we know, even there is request entering queue during the suspend
window, not a big deal, the current approach still works fine.
Thanks,
Ming
