On Wed, Oct 09, 2019 at 09:05:26AM -0700, Bart Van Assche wrote: > On 10/9/19 2:32 AM, Ming Lei wrote: > > @@ -354,7 +354,8 @@ void scsi_device_unbusy(struct scsi_device *sdev, > > struct scsi_cmnd *cmd) > > if (starget->can_queue > 0) > > atomic_dec(&starget->target_busy); > > - atomic_dec(&sdev->device_busy); > > + if (!blk_queue_nonrot(sdev->request_queue)) > > + atomic_dec(&sdev->device_busy); > > } > > Hi Ming, > > Does this patch impact the meaning of the queue_depth sysfs attribute (see > also sdev_store_queue_depth()) and also the queue depth ramp up/down > mechanism (see also scsi_handle_queue_ramp_up())? Have you considered to
This patch only ignores to track inflight SCSI commands on each LUN, so it doesn't affect the meaning of sdev->queue_depth, which is just bypassed for SSD. > enable/disable busy tracking per LUN depending on whether or not > sdev->queue_depth < shost->can_queue? Yeah, we can do it, but that isn't contradictory with this patch, :-) And we can do it even though sdev->queue_depth < shost->can_queue. Usually sdev->queue_depth is used for the following reasons: 1) this limit isn't a hard limit, which may improve IO merge with cost of IO latency. 2) fair dispatch among LUNs. This patch just tries to not apply per-LUN queue depth for SSD, because: 1) fair dispatch has been done by blk-mq in allocating driver tag 2) IO merge doesn't play big role for SSD, and IO latency can be increased by applying per-LUN queue depth. 3) NVMe doesn't apply per-ns queue depth > > The megaraid and mpt3sas drivers read sdev->device_busy directly. Is the > current version of this patch compatible with these drivers? For megaraid, sdev->device_busy is checked for choosing reply queue, this way shouldn't be better than using default managed IRQ's mapping. Similar usage is done on _base_get_high_iops_msix_index(). The only effect may be in scsih_dev_reset(), and 'SUCCESS' message is dumped even though there is in-flight command on this LUN, but it can be fixed easily. Thanks, Ming
