Re: [Xen-devel] [PATCH 17/24] xen: credit2: soft-affinity awareness in runq_tickle()

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Wed, 2016-09-07 at 14:24 +0100, anshul makkar wrote:
> On 05/09/16 15:55, Dario Faggioli wrote:
> > On Thu, 2016-09-01 at 11:52 +0100, anshul makkar wrote:
> > So, yes, we know already that it's running in a cpu at least from
> > its
> > hard affinity, what is it exactly that you are not understanding?
> If I put it simply ,  can  (X being a vcpu)
> x {soft affinity pcpus} Intersect x { hard affinity pcpu} -> be Null
> or 
> disjoint set ?
> and
> 
The user can setup things such that:

 soft-affinity{X} intersection hard-affinity{X} = O

but this, here inside the scheduler, is considered like X does not have
any soft-affinity at all, i.e., only X's hard-affinity is considered,
and all the balancing steps and operations and consideration related to
soft-affinity are ignored/skipped.

That's because it's absolutely pointless to try figure out where to
execute X, among the set of the pCPUs it prefers to run on, if it
_can't_ actually run on any pCPU from that same set.

So the answer to your question is: "it seems to be possible for the
intersection to be void, but in practise, it is not." :-)

> x{runnable pcpu} intersect (x{hard affinity pcpu} union x{soft
> affinity 
> pcpu} ) -> be null or disjoint ??
> 
I still don't get this. In particular, I'm not sure what
'x{runnable pcpu}' is. Also the union of a vcpu's soft and hard
affinity is never done (it's, as explained above, the intersection that
counts).

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

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