WARNING - OLD ARCHIVES

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/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: RE: [Xen-devel] poor domU VBD performance.

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: RE: [Xen-devel] poor domU VBD performance.
From: Kurt Garloff <garloff@xxxxxxx>
Date: Tue, 29 Mar 2005 15:34:08 +0200
Cc: Peter Bier <peter_bier@xxxxxx>, Andrew Theurer <habanero@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Tue, 29 Mar 2005 13:34:16 +0000
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <A95E2296287EAD4EB592B5DEEFCE0E9D1E38CC@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Organization: SUSE/Novell
References: <A95E2296287EAD4EB592B5DEEFCE0E9D1E38CC@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mutt/1.5.6i
Hi,

On Mon, Mar 28, 2005 at 09:14:10PM +0100, Ian Pratt wrote:
> > Is the second disk exactly the same as the first one?  I'll 
> > try an IO test 
> > here on the same disk array with dom0 and domU and see what I get.
> 
> I've reproduced the problem and its a real issue. 
> 
> It only affects reads, and is almost certainly down to how the blkback
> driver passes requests down to the actual device.

Two points to look at:
* Block size (filesystems set this to 4k normally, default it 1k)
* Read ahead (you need to do it, otherwise you end up doing tiny
  requests). You can tune it in sysfs.

Regards,
-- 
Kurt Garloff, Director SUSE Labs, Novell Inc.

Attachment: pgpi4bE2QGkLg.pgp
Description: PGP signature

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel