This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empt

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and qemu-xen: support empty write barriers in xen_disk
From: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Date: Thu, 25 Nov 2010 19:30:08 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, qemu-devel@xxxxxxxxxx, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Delivery-date: Thu, 25 Nov 2010 11:30:54 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <m2n.s.1PLKM9-000VR4@xxxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Newsgroups: chiark.mail.xen.devel
References: <alpine.DEB.2.00.1011241305080.2373@kaball-desktop> <20101124165835.GF31124@xxxxxx> <4CED5700.9070204@xxxxxxxx> <m2n.s.1PLKM9-000VR4@xxxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Christoph Hellwig writes ("Re: [Xen-devel] Re: [Qemu-devel] [PATCH] qemu and 
qemu-xen: support empty write barriers in xen_disk"):
> On Wed, Nov 24, 2010 at 10:18:40AM -0800, Jeremy Fitzhardinge wrote:
> > Linux wants is a useful thing to do and implement (especially since it
> > amounts to standardising the ?BSD extension).  I'm not sure of their
> > precise semantics (esp WRT ordering), but I think its already OK.
> The nice bit is that a pure flush does not imply any odering at all.
> Which is how the current qemu driver implements the barrier requests
> anyway, so that needs some fixing.

Thanks for your comments.  Does that mean, though, that Stefano's
patch is actually making the situation worse, or simply that it isn't
making it as good as it should be ?

If it's an improvement it should be applied it even if it's not
perfect, and it sounds to me like we don't want to wait for the more
complicated discussion to finish and produce code ?


Xen-devel mailing list

<Prev in Thread] Current Thread [Next in Thread>