linux-kernel - Re: [Xen-devel] Re: [PATCH v3] xen block backend.

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Message-ID: <20110421080411.GA8969@infradead.org>
Date:	Thu, 21 Apr 2011 04:04:12 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"jaxboe@...ionio.com" <jaxboe@...ionio.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"konrad@...nel.org" <konrad@...nel.org>
Subject: Re: [Xen-devel] Re: [PATCH v3] xen block backend.

On Thu, Apr 21, 2011 at 08:28:45AM +0100, Ian Campbell wrote:
> On Thu, 2011-04-21 at 04:37 +0100, Christoph Hellwig wrote:
> > This should sit in userspace.  And last time was discussed the issue
> > Stefano said the qemu Xen disk backend is just as fast as this kernel
> > code.  And that's with an not even very optimized codebase yet.
> 
> Stefano was comparing qdisk to blktap. This patch is blkback which is a
> completely in-kernel driver which exports raw block devices to guests,
> e.g. it's very useful in conjunction with LVM, iSCSI, etc. The last
> measurements I heard was that qdisk was around 15% down compared to
> blkback.

Please show real numbers on why adding this to kernel space is required.

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