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Re: [PATCH] Xen: credit2: avoid picking a spurious idle unit when caps are used

On Wed, 2021-08-04 at 17:13 +0200, Jan Beulich wrote:
> On 04.08.2021 15:28, Dario Faggioli wrote:
> > 
> > So, was it this you were asking about and, if yes, does this answer
> > your concerns?
> Yes, it does. 
Ok, great. :-)

> I continue to think though that the "yield" variable
> could do with either a comment along the lines of what you've
> explained, or with it getting set to true in more cases (as
> indicated), as the interaction with the credit comparisons isn't
> very obvious right now (to me at least).
Fine. This is not for this patch, of course. But I'll make a note about
it, and think how to restructure the code to make it easier to
understand, in a followup patch.

> > With either my code or above the suggested form, we don't, but we
> > may
> > have to do at least the priority check for all the elements of the
> > runqueue. This was something I knew, and as a matter of fact, it
> > should
> > be quick enough (and comparable with doing expensive checks even on
> > just 1 vCPU). But still, it's ugly.
> > 
> > However, we know that the runqueue is sorted by credits!
> Oh - I was first thinking it might be, but seeing all the logic I
> (wrongly, as you now tell me) inferred it's unsorted.
Yeah, it certainly wasn't evident, from how the patch was done.

Thanks for your comment, that actually made it realize that I could do
things like that, and indeed with even so much less code churn!

Dario Faggioli, Ph.D
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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