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

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Message-ID: <20131120080440.GA13147@infradead.org>
Date:	Wed, 20 Nov 2013 00:04:40 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>
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 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?

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