Re: [PATCH 04 of 11 v3] xen: sched_credit: let the scheduler know about node-affinity

[Dario Faggioli <dario.faggioli@citrix.com>]

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On mar, 2013-03-12 at 15:57 +0000, Ian Campbell wrote:
> On Fri, 2013-02-01 at 11:01 +0000, Dario Faggioli wrote:
> > As vcpu-affinity tells where VCPUs must run, node-affinity tells
> > where they should or, better, prefer.
> 
> I cannot parse this sentence. Is the "or, better," redundant?
> 
I see... It's indeed redundant and it's a wording we sometime use in
Italian, and translating it literally is not so much of a good idea, I
guess. :-)

How about "vcpu-affinity tells where VCPUs must run, node-affinity tells
where they prefer to."

> >  While respecting vcpu-affinity
> > remains mandatory, node-affinity is not that strict, it only expresses
> > a preference, although honouring it is almost always true that will
> > bring significant performances benefit
> 
> I can't parse this last bit either ("although...benefit"). If I drop the
> "is almost always true that" it makes sense and I think expresses what
> you meant. 
>
Right, my original form was missing something, but I like your version
(i.e., removing the "is almost...that" part) better. I'll go for it.

> And just a nit, it is "performance benefits".
> 
EhEh... George explained me this "performance" VS "performances" thing
two times already, but so far I've always been able to always pick the
_wrong_ one quite effectively! :-/

> >  (especially as compared to
> > not having any affinity at all).
> > 
> > This change modifies the VCPU load balancing algorithm (for the
> > credit scheduler only), introducing a two steps logic.
> > During the first step, we use the node-affinity mask. The aim is
> > giving precedence to the CPUs where it is known to be preferable
> > for the domain to run. If that fails in finding a valid PCPU, the
> > node-affinity is just ignored and, in the second step, we fall
> > back to using cpu-affinity only.
> 
> I think from previous paragraphs that you mean to say that the first
> path takes into account node and vcpu affinity while the second only
> vcpu affinity? The above reads as if it only uses the node affinity on
> the first pass.
>
Yes, first pass uses the intersection of the two. I'll put the sentence
in a way that makes this more evident.

Thanks,
Dario

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