Re: [Xen-devel] RFC: automatic NUMA placement

To:	Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject:	Re: [Xen-devel] RFC: automatic NUMA placement
From:	Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Date:	Fri, 17 Sep 2010 08:26:24 +0200
Cc:	xen-devel@xxxxxxxxxxxxxxxxxxx
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On 09/16/10 17:52, Dan Magenheimer wrote:

I am in favor of this being optional rather than default.
It is another case of the tradeoff between performance
and flexibility that I have ranted about several times
on xen-devel, and Xen's policy seems to be fairly random
(sometimes Xen chooses performance over flexibility and
sometimes the opposite).

I went looking through xen-devel archives for a previous
discussion on this (and to find when the code got added)
but couldn't find it... if you have links to the patch
and discussion, please post.


Took a while to find it, but hg log helped :-)

Patch:http://xenbits.xensource.com/staging/xen-unstable.hg?diff/b58180cf8ab8/tools/python/xen/xend/XendDomainInfo.py

Discussion:http://lists.xensource.com/archives/html/xen-devel/2008-02/msg00883.html

-----Original Message-----
From: Juergen Gross [mailto:juergen.gross@xxxxxxxxxxxxxx]
Sent: Thursday, September 16, 2010 7:39 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] RFC: automatic NUMA placement

Hi,

I just stumbled upon the automatic pinning of vcpus on domain creation
in
case of NUMA.
This behaviour is questionable IMO, as it breaks correct handling of
scheduling weights on NUMA machines.
I would suggest to switch this feature off per default and make it a
configuration option of xend. It would make sense, however, to change
cpu pool
processor allocation to be NUMA-aware.
Switching NUMA off via boot option would remove NUMA-optimized memory
allocation, which would be sub-optimal :-)

What do you think?



Juergen

--
Juergen Gross                 Principal Developer Operating Systems
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Re: [Xen-devel] RFC: automatic NUMA placement