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] Xen 3.4.1 NUMA support

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, Andre Przywara <andre.przywara@xxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Xen 3.4.1 NUMA support
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Date: Fri, 13 Nov 2009 15:38:51 +0000
Accept-language: en-US
Acceptlanguage: en-US
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Papagiannis, Anastasios <apapag@xxxxxxxxxxxx>
Delivery-date: Fri, 13 Nov 2009 07:39:46 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <C7231E4A.1A0AC%keir.fraser@xxxxxxxxxxxxx>
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>
References: <4AFD69D9.4090204@xxxxxxx> <C7231E4A.1A0AC%keir.fraser@xxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Acpka8hyvjmh8aK2SjOZPJzudwcnGAAAjnG3AAI9rSA=
Thread-topic: [Xen-devel] Xen 3.4.1 NUMA support
> > Keir, I will check if dropping the node containment in the CPU
> > overcommitment case is an option, but what would be the right strategy
> > in that case?
> > Warn the user?
> > Don't contain at all?
> > Contain to more than onde node?
> I would suggest simply don't contain at all (i.e., keep equivalent
> numa=off
> behaviour) would be safest.

I disagree. In systems with 2 nodes it will use all nodes, which is the same as 
your propose[*]. In systems with more nodes it will do placement to some 
subset. Note that systems with >2 nodes generally have stronger NUMA effects 
and these are exactly the systems where node placement is a good thing.

[*] note that numa=off is quite different from just disabling node placement. 
If node placement is disabled we still get the benefit of memory striping 
across nodes, which at least avoids some performance cliffs.


Xen-devel mailing list