Re: [RFC PATCH V4 2/2] scsi: core: don't limit per-LUN queue depth for SSD

[Bart Van Assche]

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 enable/disable busy tracking per LUN depending on whether 
or not sdev->queue_depth < shost->can_queue?

The megaraid and mpt3sas drivers read sdev->device_busy directly. Is the 
current version of this patch compatible with these drivers?

Thanks,

Bart.