On Fri, Oct 18, 2019 at 12:00:07AM +0530, Kashyap Desai 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 > > 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? > > We need to know per scsi device outstanding in mpt3sas and megaraid_sas > driver. Is the READ done in fast path or slow path? If it is on slow path, it should be easy to do via blk_mq_in_flight_rw(). > Can we get supporting API from block layer (through SML) ? something > similar to "atomic_read(&hctx->nr_active)" which can be derived from > sdev->request_queue->hctx ? > At least for those driver which is nr_hw_queue = 1, it will be useful and we > can avoid sdev->device_busy dependency. If you mean to add new atomic counter, we just move the .device_busy into blk-mq, that can become new bottleneck. thanks, Ming
