On 2020-09-09 00:29, Ming Lei wrote:
> + if (old) {
> + /*
> + * ->restarts has to be kept as non-zero if there is
> + * new budget contention comes.
> + *
> + * No need to run queue when either another re-run
> + * queue wins in updating ->restarts or one new budget
> + * contention comes.
> + */
> + if (atomic_cmpxchg(&sdev->restarts, old, 0) == old)
> + blk_mq_run_hw_queues(sdev->request_queue, true);
How about combining the above two if-statements into a single if-statement to
keep the indentation level low?
> /* Returns false when no more bytes to process, true if there are more */
> @@ -1611,8 +1630,32 @@ static void scsi_mq_put_budget(struct request_queue *q)
> static bool scsi_mq_get_budget(struct request_queue *q)
> {
> struct scsi_device *sdev = q->queuedata;
> + int ret = scsi_dev_queue_ready(q, sdev);
>
> - return scsi_dev_queue_ready(q, sdev);
> + if (ret)
> + return true;
I like Ewan's comment about the above code:
"I think this should just be:
if (scsi_dev_queue_ready(q, sdev))
return true;
There's no particular reason to call the function in a local variable
initializer, this just makes the code less clear to me. And "ret"
isn't needed for any other reason."
> + /*
> + * If all in-flight requests originated from this LUN are completed
> + * before setting .restarts, sdev->device_busy will be observed as
> + * zero, then blk_mq_delay_run_hw_queues() will dispatch this request
> + * soon. Otherwise, completion of one of these request will observe
> + * the .restarts flag, and the request queue will be run for handling
> + * this request, see scsi_end_request().
> + */
> + if (unlikely(atomic_read(&sdev->device_busy) == 0 &&
> + !scsi_device_blocked(sdev)))
> + blk_mq_delay_run_hw_queues(sdev->request_queue, SCSI_QUEUE_DELAY);
The above comment doesn't explain what happens if the all pending SCSI
commands complete after .restarts has been incremented and before .device_busy
is read. Since I think that case is handled, consider changing "before setting
.restarts" into "before reading .device_busy".
Anyway, since I think the code is fine, feel free to add:
Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
