From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Borntraeger <borntraeger@de.ibm.com>
Subject: Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support
Date: Wed, 29 Apr 2009 13:19:04 +0200
Message-ID: <200904291319.05247.borntraeger@de.ibm.com>
References: <20090427082606.GA32604@lst.de> <20090429104854.GA7846@lst.de> <200904291211.20374.paul@codesourcery.com>
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Cc: qemu-devel@nongnu.org, Christoph Hellwig <hch@lst.de>,
	Anthony Liguori <anthony@codemonkey.ws>, kvm@vger.kernel.org,
	Rusty Russell <rusty@rustcorp.com.au>,
	Hannes Reinecke <hare@suse.de>
To: Paul Brook <paul@codesourcery.com>
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In-Reply-To: <200904291211.20374.paul@codesourcery.com>
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Am Wednesday 29 April 2009 13:11:19 schrieb Paul Brook:
> On Wednesday 29 April 2009, Christoph Hellwig wrote:
> > On Tue, Apr 28, 2009 at 11:37:01AM -0500, Anthony Liguori wrote:
> > > Ah, excellent.  I think that's a great thing to do.  So do you think
> > > virtio-scsi would deprecate virtio-blk?
> >
> > I don't think so.  If you have an image format or a non-scsi blockdevice
> > underneath virtio-block avoids the encoding into SCSI CDBs and back and
> > should be faster.
> 
> Is this actually measurably faster, or just infinitesimally faster in 
> theory? 

If the underlying backing is 4k block size and the emulated scsi disk has 512 byte block size, write performance can be a lot slower.