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

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

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.

> -----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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