Re: [Xen-devel] [PATCH 1/4] xen: credit2: implement utilization cap

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Tue, 2017-07-25 at 15:34 +0100, George Dunlap wrote:
> On 06/29/2017 11:09 AM, Dario Faggioli wrote:
> > E.g., if the vcpu is "greedy", and always tries to run, as soon as
> > it
> > has some budget, the difference between the two solution is _where_
> > we
> > put the "sitting period".
> 
> Sorry, dropped this thread to prepare for XenSummit.
> 
NP.

> Well I think there's a principle a bit like Ockham's Razor: In
> general,
> if there's not an obvious advantage between two implementations, the
> simpler / easier to understand implementation is better.
> 
> My sense is also that in general, as long as context switching
> overhead
> doesn't become an issue, allowing a guest to run for shorter bursts
> more
> often is better than allowing it to run for longer bursts less
> often.  A
> cpu-bound task will perform about as well in both cases, but a
> latency-sensitive task will perform much worse if it's allowed to
> burn
> up its timeslice and forced to wait for a big chunk of time.
> 
That's actually a fair point.

> On the other hand, my intuitions about how to improve AFL fuzzing
> these
> last few weeks have turned out to be consistently wrong, so at the
> moment I'm not inclined to be overly confident in my intuition
> without
> some testing. :-)
> 
Well, this is a similar situation to the one in the other thread. It's
an edge case that, likely, will never or only very rarely occur. So, we
don't need to think too much about it, and we well even afford to
follow your intuition! :-D

Mmm... Maybe this came out a bit less of a "cheering you up", as I
wanted it to be, but hey, I tried! :-P :-P :-P

No, jokes apart, I like your argument about the effect this may have on
latency sensitive workload, if they happen to suffer from one of this
overrun, so I will change the code the way you suggest. :-)

Thanks and 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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