Re: [Xen-devel] RFC: Still TODO for 4.2? xl domain numa memory allocation vs xm/xend

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Jan 20, 2012 at 07:59:28AM +0000, Ian Campbell wrote:
> On Thu, 2012-01-19 at 21:14 +0000, Pasi Kärkkäinen wrote:
> > On Wed, Jan 04, 2012 at 04:29:22PM +0000, Ian Campbell wrote:
> > > 
> > > Has anybody got anything else? I'm sure I've missed stuff. Are there any
> > > must haves e.g. in the paging/sharing spaces?
> > > 
> > 
> > Something that I just remembered:
> > http://wiki.xen.org/xenwiki/Xen4.1
> > 
> > "NUMA-aware memory allocation for VMs. xl in Xen 4.1 will allocate
> > equal amount of memory from every NUMA node for the VM. xm/xend
> > allocates all the memory from the same NUMA node."
> 
> I'm not that familiar with the NUMA support but my understanding was
> that memory was allocated by libxc/the-hypervisor and not by the
> toolstack and that the default was to allocate from the same numa nodes
> as domains the processor's were pinned to i.e. if you pin the processors
> appropriately the Right Thing just happens. Do you believe this is not
> the case and/or not working right with xl?
> 
> CCing Juergen since he added the cpupool support and in particular the
> cpupool-numa-split option so I'm hoping he knows something about NUMA
> more generally.
> 
> > Is this something that should be looked at?
>  
> Probably, but is anyone doing so?
> 
> > Should the numa memory allocation be an option so it can be controlled
> > per domain? 
> 
> What options did xm provide in this regard?
> 
> Does xl's cpupool (with the cpupool-numa-split option) server the same
> purpose?
> 
> > The default libxl behaviour might cause unexpected performance issues
> > on multi-socket systems? 
> 
> I'm not convinced libxl is behaving any different to xend but perhaps
> someone can show me the error of my ways.
> 


See this thread: 
http://old-list-archives.xen.org/archives/html/xen-devel/2011-07/msg01423.html

where Stefano wrote:
"I think we forgot about this feature but it is important and hopefully
somebody will write a patch for it before 4.2 is out."


-- Pasi


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