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SubjectRe: [PATCH 2/2] null_blk: restart request processing on completion handler
From
2015-06-02 8:35 GMT+09:00 Akinobu Mita <akinobu.mita@gmail.com>:
> When irqmode=2 (IRQ completion handler is timer) and queue_mode=1
> (Block interface to use is rq), the completion handler should restart
> request handling for any pending requests on a queue because request
> processing stops when the number of commands are queued more than
> hw_queue_depth (null_rq_prep_fn returns BLKPREP_DEFER).
>
> Without this change, the following command cannot finish.
>
> # modprobe null_blk irqmode=2 queue_mode=1 hw_queue_depth=1
> # fio --name=t --rw=read --size=1g --direct=1 \
> --ioengine=libaio --iodepth=64 --filename=/dev/nullb0
>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: Jens Axboe <axboe@fb.com>
> ---
> drivers/block/null_blk.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
> index 6f0a58e..6f9b753 100644
> --- a/drivers/block/null_blk.c
> +++ b/drivers/block/null_blk.c
> @@ -243,6 +243,17 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
> cmd = container_of(entry, struct nullb_cmd, ll_list);
> entry = entry->next;
> end_cmd(cmd);
> +
> + if (cmd->rq) {
> + struct request_queue *q = cmd->rq->q;
> +
> + if (!q->mq_ops && blk_queue_stopped(q)) {
> + spin_lock(q->queue_lock);
> + if (blk_queue_stopped(q))
> + blk_start_queue(q);

Should 'blk_start_queue(q)' be:

queue_flag_clear(QUEUE_FLAG_STOPPED, q);
blk_run_queue_async(q);
?

Otherwise, all pending requests on a queue are completed by this timer
handler execution without needing next timer expiry.

> + spin_unlock(q->queue_lock);
> + }
> + }
> } while (entry);
> }
>
> @@ -334,6 +345,7 @@ static int null_rq_prep_fn(struct request_queue *q, struct request *req)
> req->special = cmd;
> return BLKPREP_OK;
> }
> + blk_stop_queue(q);
>
> return BLKPREP_DEFER;
> }
> --
> 1.9.1
>


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