Re: [PATCH v2 4/4] scsi-mq: Reduce suspend latency

Ming Lei
2017-09-21T22:06:54Z

On Thu, Sep 21, 2017 at 02:22:55PM -0700, Bart Van Assche wrote:
> Avoid that it can take 200 ms too long to wait for ongoing requests
> to finish. Note: blk_mq_freeze_queue() uses a wait queue to wait
> for ongoing requests to finish.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Martin K. Petersen <martin.petersen@oracle.com>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> ---
> drivers/scsi/scsi_lib.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index e76fd6e89a81..34e5f0f95d01 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -2901,10 +2901,15 @@ scsi_device_quiesce(struct scsi_device *sdev)
> if (err)
> return err;
>
> - scsi_run_queue(q);
> - while (atomic_read(&sdev->device_busy)) {
> - msleep_interruptible(200);
> + if (q->mq_ops) {
> + blk_mq_freeze_queue(q);
> + blk_mq_unfreeze_queue(q);

As I commented in another patch, you don't check the 'preempt only'
flag in normal I/O path, then from now on, any I/O can come.

> + } else {
> scsi_run_queue(q);
> + while (atomic_read(&sdev->device_busy)) {
> + msleep_interruptible(200);
> + scsi_run_queue(q);
> + }

Are you sure only blk-mq need to drain queue? We need
to do that for block legacy too.

--
Ming