Re: [PATCH RESEND 05/12] xen: numa-sched: make space for per-vcpu node-affinity

[George Dunlap <george.dunlap@eu.citrix.com>]

On 06/11/13 14:26, Dario Faggioli wrote:
> On mer, 2013-11-06 at 11:44 +0000, George Dunlap wrote:
>> On 06/11/13 10:00, Dario Faggioli wrote:
>>> I see, and that sounds sensible to me... It's mostly a matter a matter
>>> of deciding whether o not we want something like that, and, if yes,
>>> whether we want it based on hard of soft.
>>>
>>> Personally, I think I agree with you on having it based on hard
>>> affinities by default.
>>>
>>> Let's see if George get to say something before I get to that part of
>>> the (re)implementation. :-)
>> I would probably have it based on soft affinities, since that's where we
>> expect to have the domain's vcpus actually running most if the time;
>>
> True. However, doing that would rule out cpupool and vcpu-pinning.

I guess I was assuming that a vcpu's soft affinity would always be 
considered a subset of its hard affinity and the cpus in its cpupool.

>> I think for now I might advise putting off doing a NUMA interface at the
>> libxl level, and do a full vNUMA interface in another series (perhaps
>> for 4.5, depending on the timing).
>>
> Well, I agree that all this is of very little use without vNUMA, but at
> the same time, it's not necessarily only useful for it. Also, whatever
> it is vcpu-node-affinity or soft-affinity, if it is not wired up
> properly up to the higher layers, there's very few point of having the
> HV part only... So my idea was to redo and resend everything, including
> libxl and xl bits.
>
> Of course, that doesn't mean we must necessarily have this for 4.4
> (although I think it would still be feasible), just that we either
> check-in or wait for both the implementation and the interface. Again,
> how's the updated release schedule?

Well we definitely should plumb through access to the soft affinity 
directly through libxl.  The question is whether it would be useful to 
have a libxl per-vcpu *numa* affinity that is not yet a full vNUMA 
implementation.  If long-term we want to have vcpu -> vnode, and then 
vnode->pnode, the having a direct vcpu->pnode interface in the interim 
is probably not particularly useful, I don't think.

Re the release schedule: we agreed to move the code freeze to November 
18, so we've got just under two weeks.  I think keeping the libxl side 
simple will allow us to at least get the "soft affinity" stuff in for 
4.4, whether the vNUMA stuff makes it or not.

  -George