On Thu, Jul 12, 2018 at 05:58:28PM +0800, Ming Lei wrote:
> On Thu, Jul 12, 2018 at 12:29:05AM +0800, Ming Lei wrote:
> > This patch introduces blk_mq_pm_add_request() which is called after
> > allocating one request. Also blk_mq_pm_put_request() is introduced
> > and called after one request is freed.
> >
> > For blk-mq, it can be quite expensive to accounting in-flight IOs,
> > so this patch calls pm_runtime_mark_last_busy() simply after each IO
> > is done, instead of doing that only after the last in-flight IO is done.
> > This way is still workable, since the active non-PM IO will be checked
> > in blk_pre_runtime_suspend(), and runtime suspend will be prevented
> > if there is any active non-PM IO.
> >
> > Also makes blk_post_runtime_resume() to cover blk-mq.
> >
> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> > Cc: linux-pm@xxxxxxxxxxxxxxx
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Bart Van Assche <bart.vanassche@xxxxxxx>
> > Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxxxx>
> > Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
> > Cc: linux-scsi@xxxxxxxxxxxxxxx
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> > block/blk-core.c | 12 ++++++++++--
> > block/blk-mq.c | 24 ++++++++++++++++++++++++
> > 2 files changed, 34 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index c4b57d8806fe..bf66d561980d 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -3804,12 +3804,17 @@ EXPORT_SYMBOL(blk_pm_runtime_init);
> > int blk_pre_runtime_suspend(struct request_queue *q)
> > {
> > int ret = 0;
> > + bool active;
> >
> > if (!q->dev)
> > return ret;
> >
> > spin_lock_irq(q->queue_lock);
> > - if (q->nr_pending) {
> > + if (!q->mq_ops)
> > + active = !!q->nr_pending;
> > + else
> > + active = !blk_mq_pm_queue_idle(q);
> > + if (active) {
> > ret = -EBUSY;
> > pm_runtime_mark_last_busy(q->dev);
> > } else {
>
> Looks there is one big issue, one new IO may come just after reading
> 'active' and before writing RPM_SUSPENDING to q->rpm_status, and both
> the suspending and the new IO may be in-progress at the same time.
One idea I thought of is to use seqlock to sync changing & reading q->rpm_status,
and looks read lock(read_seqcount_begin/read_seqcount_retry) shouldn't introduce
big cost in fast path.
Thanks,
Ming
