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

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Date:	Sun, 12 Jul 2015 10:00:14 +0800
From:	Bob Liu <bob.liu@...cle.com>
To:	Jens Axboe <axboe@...com>
CC:	linux-kernel@...r.kernel.org, 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 07/12/2015 02:14 AM, Jens Axboe wrote:
> 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.
> 

Right, but there are memory consumption and migration issues while using more hardware queues.
So I separated this patch from that big patchset and hope can be merged first.

>> 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.
> 

Will send v3.

>> Signed-off-by: Arianna Avanzini <avanzini.arianna@...il.com>
>> Signed-off-by: Bob Liu <bob.liu@...cle.com>
> 
> Acked-by: Jens Axboe <axboe@...com>
> 

Thank you!

-- 
Regards,
-Bob
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