Re: [PATCH 03 of 10 v2] xen: sched_credit: let the scheduler know about node-affinity

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

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On Thu, 2012-12-20 at 07:44 +0100, Juergen Gross wrote: 
> Am 19.12.2012 20:07, schrieb Dario Faggioli:
> > [...] 
> >
> > 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.
> >
> > Signed-off-by: Dario Faggioli<dario.faggioli@citrix.com>
> > ---
> > Changes from v1:
> >   * CPU masks variables moved off from the stack, as requested during
> >     review. As per the comments in the code, having them in the private
> >     (per-scheduler instance) struct could have been enough, but it would be
> >     racy (again, see comments). For that reason, use a global bunch of
> >     them of (via per_cpu());
> 
> Wouldn't it be better to put the mask in the scheduler private per-pcpu area?
> This could be applied to several other instances of cpu masks on the stack,
> too.
> 
Yes, as I tired to explain, if it's per-cpu it should be fine, since
credit has one runq per each CPU and hence runq lock is enough for
serialization.

BTW, can you be a little bit more specific about where you're suggesting
to put it? I'm sorry but I'm not sure I figured what you mean by "the
scheduler private per-pcpu area"... Do you perhaps mean making it a
member of `struct csched_pcpu' ?

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)



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