Re: [PATCH] SCSI: run queue if SCSI device queue isn't ready and queue is idle

[Johannes Thumshirn]

[ +Cc Omar ]

Ming Lei <ming.lei@xxxxxxxxxx> writes:
> Before commit 0df21c86bdbf ("scsi: implement .get_budget and .put_budget
> for blk-mq"), we run queue after 3ms if queue is idle and SCSI device
> queue isn't ready, which is done in handling BLK_STS_RESOURCE. After
> commit 0df21c86bdbf is introduced, queue won't be run any more under
> this situation.
>
> IO hang is observed when timeout happened, and this patch fixes the IO
> hang issue by running queue after delay in scsi_dev_queue_ready, just like
> non-mq. This issue can be triggered by the following script[1].
>
> There is another issue which can be covered by running idle queue:
> when .get_budget() is called on request coming from hctx->dispatch_list,
> if one request just completes during .get_budget(), we can't depend on
> SCSI's restart to make progress any more. This patch fixes the race too.
>
> With this patch, we basically recover to previous behaviour(before commit
> 0df21c86bdbf) of handling idle queue when running out of resource.
>
> [1] script for test/verify SCSI timeout
> rmmod scsi_debug
> modprobe scsi_debug max_queue=1
>
> DEVICE=`ls -d /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/* | head -1 | xargs basename`
> DISK_DIR=`ls -d /sys/block/$DEVICE/device/scsi_disk/*`
>
> echo "using scsi device $DEVICE"
> echo "-1" >/sys/bus/pseudo/drivers/scsi_debug/every_nth
> echo "temporary write through" >$DISK_DIR/cache_type
> echo "128" >/sys/bus/pseudo/drivers/scsi_debug/opts
> echo none > /sys/block/$DEVICE/queue/scheduler
> dd if=/dev/$DEVICE of=/dev/null bs=1M iflag=direct count=1 &
> sleep 5
> echo "0" >/sys/bus/pseudo/drivers/scsi_debug/opts
> wait
> echo "SUCCESS"

SO I turned the above into a blktest but have found some shortcommings
of my bash skills. Maybe you or Omar has a soution for it:

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