On Wed, Jul 18, 2018 at 7:49 AM, Bart Van Assche <bart.vanass...@wdc.com> wrote: > Instead of allowing requests that are not power management requests > to enter the queue in runtime suspended status (RPM_SUSPENDED), make > the blk_get_request() caller block. This change fixes a starvation > issue: it is now guaranteed that power management requests will be > executed no matter how many blk_get_request() callers are waiting. > Instead of maintaining the q->nr_pending counter, rely on > q->q_usage_counter. Call pm_runtime_mark_last_busy() every time a > request finishes instead of only if the queue depth drops to zero. > Use RQF_PREEMPT to mark power management requests instead of RQF_PM. > This is safe because the power management core serializes system-wide > suspend/resume and runtime power management state changes. > > Signed-off-by: Bart Van Assche <bart.vanass...@wdc.com> > Cc: Christoph Hellwig <h...@lst.de> > Cc: Ming Lei <ming....@redhat.com> > Cc: Alan Stern <st...@rowland.harvard.edu> > Cc: Johannes Thumshirn <jthumsh...@suse.de> > --- > block/blk-core.c | 56 +++++++++++++++++---------------------- > block/blk-mq-debugfs.c | 1 - > block/blk-mq.c | 12 ++++----- > block/elevator.c | 11 +------- > drivers/scsi/sd.c | 4 +-- > drivers/scsi/ufs/ufshcd.c | 10 +++---- > include/linux/blk-mq.h | 1 + > include/linux/blkdev.h | 7 ++--- > 8 files changed, 41 insertions(+), 61 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index f84a9b7b6f5a..65d7f27c8c22 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1719,7 +1719,7 @@ EXPORT_SYMBOL_GPL(part_round_stats); > #ifdef CONFIG_PM > static void blk_pm_put_request(struct request *rq) > { > - if (rq->q->dev && !(rq->rq_flags & RQF_PM) && !--rq->q->nr_pending) > + if (rq->q->dev && !(rq->rq_flags & RQF_PREEMPT)) > pm_runtime_mark_last_busy(rq->q->dev); > } > #else > @@ -2737,30 +2737,6 @@ void blk_account_io_done(struct request *req, u64 now) > } > } > > -#ifdef CONFIG_PM > -/* > - * Don't process normal requests when queue is suspended > - * or in the process of suspending/resuming > - */ > -static bool blk_pm_allow_request(struct request *rq) > -{ > - switch (rq->q->rpm_status) { > - case RPM_RESUMING: > - case RPM_SUSPENDING: > - return rq->rq_flags & RQF_PM; > - case RPM_SUSPENDED: > - return false; > - } > - > - return true; > -} > -#else > -static bool blk_pm_allow_request(struct request *rq) > -{ > - return true; > -} > -#endif > - > void blk_account_io_start(struct request *rq, bool new_io) > { > struct hd_struct *part; > @@ -2806,11 +2782,12 @@ static struct request *elv_next_request(struct > request_queue *q) > > while (1) { > list_for_each_entry(rq, &q->queue_head, queuelist) { > - if (blk_pm_allow_request(rq)) > - return rq; > - > - if (rq->rq_flags & RQF_SOFTBARRIER) > - break; > + /* > + * If a request gets queued in state RPM_SUSPENDED > + * then that's a kernel bug. > + */ > + WARN_ON_ONCE(q->rpm_status == RPM_SUSPENDED); > + return rq; > } > > /* > @@ -3801,8 +3778,11 @@ int blk_pre_runtime_suspend(struct request_queue *q) > if (!q->dev) > return ret; > > + blk_set_preempt_only(q); > + blk_freeze_queue_start(q); > + > spin_lock_irq(q->queue_lock); > - if (q->nr_pending) { > + if (!percpu_ref_is_zero(&q->q_usage_counter)) {
This way can't work reliably because the percpu ref isn't in atomic mode yet after blk_freeze_queue_start() returns, then percpu_ref_is_zero() won't see accurate value of the counter, finally the device may be put down before in-flight requests are completed by hardware. Thanks, Ming Lei