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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-01-20 at 08:15 +0000, Pasi KÃrkkÃinen wrote:
> On Fri, Jan 20, 2012 at 07:59:28AM +0000, Ian Campbell wrote:
> > On Thu, 2012-01-19 at 21:14 +0000, Pasi KÃrkkÃinen 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."

Is anyone looking into this?

Does cpupool-numa-split solve this same problem?

I think I forgot to actually CC Juergen when I said, doing that now.

Ian.



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