Re: [PATCH v2] xen/blkfront: convert to blk-mq APIs

[Jens Axboe <axboe@fb.com>]

On 07/11/2015 07:30 AM, Bob Liu wrote:
> Note: This patch is based on original work of Arianna's internship for
> GNOME's Outreach Program for Women.

Great to see this finally get prepped to go in!

> Only one hardware queue is used now, so there is no performance change.

I would hope that the blk-mq path, even with one queue, is a perf win 
over the old interface. So I'm not sure that is correct. But the bigger 
win will be with more queues, of course.

> The legacy non-mq code is deleted completely which is the same as other
> drivers like virtio, mtip, and nvme.
>
> Also dropped one unnecessary holding of info->io_lock when calling
> blk_mq_stop_hw_queues().
>
> Changes in v2:
>   - Reorganized blk_mq_queue_rq()
>   - Restored most io_locks in place

Looks good to me. The most common error case is the busy-out not 
stopping queues, or not restarting them at completion. But that all 
looks fine.

I would, however, rename blk_mq_queue_rq(). It sounds like a core 
function. blkif_queue_rq() would be more appropriate.

> Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
> Signed-off-by: Bob Liu <bob.liu@oracle.com>

Acked-by: Jens Axboe <axboe@fb.com>


-- 
Jens Axboe