Re: [Xen-devel] [PATCH 03 of 11 v4] xen: sched_credit: when picking, make sure we get an idle one, if any

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On lun, 2013-03-18 at 14:02 +0000, George Dunlap wrote:
> On 15/03/13 10:55, Jan Beulich wrote:
> >>>> On 15.03.13 at 11:37, Dario Faggioli <dario.faggioli@xxxxxxxxxx> wrote:
> >> On ven, 2013-03-15 at 08:14 +0000, Jan Beulich wrote:
> >> Perhaps I can turn the condition into something like this:
> >>
> >>      if ( !cpumask_test_cpu(cpu, &cpus) )
> >>          cpu = cpumask_empty(&cpus) ? cpu : cpumask_cycle(cpu, &cpus);
> >>
> >> So that we pay the price less frequently?
> > Given cpu < nr_cpu_ids before this, yes, that sounds right. Or
> > you could simply switch the operands of the && in your original
> > if(). Yet less expensive would be if you stored the result of
> > cpumask_cycle() in another variable and copied it into "cpu"
> > only if less than nr_cpu_ids. That would eliminate the need for
> > cpumask_empty() altogether.
> 
> It seems to me like just switching the order would result in more 
> readable code.
> 
> Wouldn't hurt to add "Do the quick test first" to the comment so no one 
> switches it back. :-)
> 
Ok, will do.

Thanks,
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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