Re: [PATCH 2/2] xen: credit2: limit the max number of CPUs in a runqueue

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Thu, 2020-04-30 at 14:52 +0200, Jürgen Groß wrote:
> On 30.04.20 14:28, Dario Faggioli wrote:
> > On Thu, 2020-04-30 at 09:35 +0200, Jürgen Groß wrote:
> > > 
> > With that, when the user removes 4 CPUs, we will have the 6 vs 10
> > situation. But we would make sure that, when she adds them back, we
> > will go back to 10 vs. 10, instead than, say, 6 vs 14 or something
> > like
> > that.
> > 
> > Was something like this that you had in mind? And in any case, what
> > do
> > you think about it?
> 
> Yes, this would be better already.
> 
Right, I'll give a try at this, and let's see how it ends up looking
like.

> > This way if, in future, CPU 1 is removed from Pool-1 and added to
> > Pool-0, I am sure it can go in the same runqueue where CPU 0 is. If
> > I
> > don't consider CPUs which currently are in another pool, we risk
> > that
> > when/if they're added to this very pool, they'll end up in a
> > different
> > runqueue.
> > 
> > And we don't want that.
> > 
> Yes.
> 
Cool. :-)

> You should add a comment in this regard.
> 
Sure.

> And you should either reject the case of less cpus per queue than
> siblings per core, or you should handle this situation. Otherwise you
> won't ever find a suitable run-queue. :-)
> 
Right, and in fact I had a check for that, rejecting smaller
max-cpus-per-runqueue than siblings, where we validate also the other
scheduling parameters. But indeed it's not there now, so I guess I
removed it by mistake before sending.

And now that I double check, I'm also missing documenting the new
parameters.

Thanks and Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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