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Date: Mon, 11 Jan 2010 14:47:33 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] Re: [RFC][PATCH] performance improvement for windows
	guests, running on top of virtio block device
Message-ID: <20100111134733.GA27253@lst.de>
References: <1263195647.2005.44.camel@localhost> <4B4AE1BD.4000400@redhat.com>
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To: Avi Kivity <avi@redhat.com>
Cc: Vadim Rozenfeld <vrozenfe@redhat.com>, Dor Laor <dlaor@redhat.com>, Christoph Hellwig <hch@lst.de>, qemu-devel <qemu-devel@nongnu.org>

On Mon, Jan 11, 2010 at 03:13:53PM +0200, Avi Kivity wrote:
> As Dor points out, the call to virtio_blk_handle_output() wants to be 
> before the test for pending, so we scan the ring as early as possible

It could cause a race window where we add an entry to the ring after
we run virtio_blk_handle_output, but before re-enabling the
notification.  But I think my variant of the patch that I just posted
should deal with this in an even better way.