Re: [Xen-devel] [PATCH 1/3] libxl: check whether vcpu affinity and vnuma info match

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Mar 24, 2015 at 03:47:27PM +0000, Dario Faggioli wrote:
> On Tue, 2015-03-24 at 14:41 +0000, Wei Liu wrote:
> > On Tue, Mar 24, 2015 at 02:41:48PM +0100, Dario Faggioli wrote:
> 
> > Currently all the checks that returns error are all guest visible
> > mis-configurations. I'm trying to reason whether we should return an
> > error or just print a warning.
> > 
> > What is the outcome if you have conflicting setting in vNUMA and vcpu
> > affinity? 
> >
> The outcome is that vcpus will either always run (if hard affinity and
> vnuma info mismatch) or prefer to run (if soft affinity and vnuma info
> mismatch) on pcpus from pnode(s) different from the pnode specified in
> vnuma configuration, and hence where the memory is.
> 
> So, for instance, with this:
> 
>  vnuma = [ [ "pnode=0","size=1000","vcpus=0-1","vdistances=10,20"  ],
>            [ "pnode=1","size=1000","vcpus=2-3","vdistances=20,10"  ] ]
> 
> and this:
> 
>  cpus_soft = "node:1"
>  cpus = "node:0"
> 
> in the config file, we have a soft affinity mismatch for vcpus 0,1 and
> an hard affinity mismatch for vcpus 2,3.
> 
> This means that vcpus 0,1 can run everywhere, but they will prefer to
> run on pcpus from pnode 1, while, when the domain was built, they've
> been assigned to vnode 0, which has its memory allocated from pnode 0.
> This will (potentially) cause a lot of remote memory accesses.
> 
> It also means that vcpus 2,3 will only run on pcpus from node:0, while
> they've been assigned to vnode 1, which has its memory allocated from
> pnode 1. This will mean all memory accesses will be remote memory
> accesses
> 
> So no functional consequences, but performance will most likely be
> affected.
> 
> > I guess it's just performance penalty but nothing guest
> > visible could happen?
> > 
> Exactly.

OK. I think we can be lenient on this sort of thing. I think you also
need to add to the comment before libxl__vnuma_config_check.

With that change added:

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

> 
> Regards,
> Dario



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