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Re: [Xen-devel] [PATCH RFC v2 4/7] libxl/vNUMA: vNUMA libxl functionality.



On 09/17/2013 05:38 PM, Ian Campbell wrote:
On Tue, 2013-09-17 at 17:36 +0100, George Dunlap wrote:
On Fri, Sep 13, 2013 at 9:50 AM, Elena Ufimtseva <ufimtseva@xxxxxxxxx> wrote:
vNUMA libxl supporting functionality.
libxl supporting functionality for vNUMA includes:
* having vNUMA memory areas sizes, transforms it to
start and end pfns based on domain e820 map;
* contructs vnode_to_pnode map for vNUMA nodes memory
allocation and pass it to Xen; the mechanism considers
automatic NUMA placement in case of presence of hardware
NUMA; In best case scenario all vnodes will be allocated
within one pnode. If the domain spans different pnodes,
the vnodes will be one-by-one placed to pnodes. If such
allocation is impossible due to the memory constraints,
the allocation will use default mechanism; this is worst
case scenario.

Why would someone want to make a VM with two vnodes and then put them
on the same pnode?  Apart from testing, of course, but our defaults
should be for the common case of real users.

If your pool of machines included 1- and 2-node systems might you want
to do this so that when you migrate the vm to a two node system it can
make use of it?

Yes, but from the description (and from a brief glance at the code) it looks like if it can happen to fit all the vnodes on a single pnode, it will do so -- even if the node affinity for the domain spans several nodes.

I think if I was a user, and made a VM with 2 vnodes, and then set its node affinity to two pnodes, I would expect the tools to place each vnode on one pnode.

At this point it may be bike-shedding, though... at some point we'll have the ability to specify node affinity for individual vcpus, at which time we can specify a pnode affinity for individual vnodes. As long as we have something not barking mad here, we can revisit it before the release (as long as someone writes down to do it).

 -George

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