linux-kernel - Re: [Regression x2, 3.13-git] virtio block mq hang, iostat busted on virtio devices

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Message-ID: <528CE13D.3000907@kernel.dk>
Date:	Wed, 20 Nov 2013 09:20:13 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org
Subject: Re: [Regression x2, 3.13-git] virtio block mq hang, iostat busted
 on virtio devices

On 11/20/2013 01:04 AM, Christoph Hellwig wrote:
> On Tue, Nov 19, 2013 at 02:43:51PM -0700, Jens Axboe wrote:
>> No, the nr_requests isn't actually relevant in the blk-mq context, the
>> driver sets its own depth. For the above, it's 64 normal commands, and 2
>> reserved. The reserved would be for a flush, for instance. If someone
>> attempts to queue more than the allocated number of requests, it'll stop
>> the blk-mq queue and kick things into gear on the virtio side. Then when
>> requests complete, we start the queue again.
> 
> Btw, any reason we lowerered the queue depth from 128 to 64 in
> virtio-blk?

No, we can easily bump it to 128 again, I think it was a leftover from
where it had more queues and testing.

-- 
Jens Axboe

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