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

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Message-ID: <55A15D22.4020709@fb.com>
Date:	Sat, 11 Jul 2015 12:14:58 -0600
From:	Jens Axboe <axboe@...com>
To:	Bob Liu <bob.liu@...cle.com>, <linux-kernel@...r.kernel.org>
CC:	<hch@...radead.org>, <xen-devel@...ts.xenproject.org>,
	<avanzini.arianna@...il.com>, <david.vrabel@...rix.com>,
	<konrad.wilk@...cle.com>, <marcus.granado@...rix.com>,
	<roger.pau@...rix.com>
Subject: Re: [PATCH v2] xen/blkfront: convert to blk-mq APIs

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@...il.com>
> Signed-off-by: Bob Liu <bob.liu@...cle.com>

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


-- 
Jens Axboe

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