Re: Xen optimization

[Dario Faggioli <dfaggioli@suse.com>]

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On Fri, 2018-10-19 at 14:02 -0700, Stefano Stabellini wrote:
> On Wed, 17 Oct 2018, Milan Boberic wrote:
> > I checked interrupt frequency with oscilloscope
> > just to be sure (toggling LED on/off when interrupts occur). So,
> > when I set:
> > - interrupts to be generated every 8 us I get jitter of 6 us
> > - interrupts to be generated every 10 us I get jitter of 3 us
> > (after
> > 2-3mins it jumps to 6 us)
> > - interrupts to be generated every 15 us jitter is the same as when
> > only bare-metal application runs on board (without Xen or any OS)
> 
> These are very interesting numbers! 
>
Indeed.

> Thanks again for running these
> experiments. I don't want to jump to conclusions but they seem to
> verify
> the theory that if the interrupt frequency is too high, we end up
> spending too much time handling interrupts, the system cannot cope,
> hence jitter increases.
> 
Yep, this makes a lot of sense.

> However, I would have thought that the threshold should be lower than
> 15us, given that it takes 2.5us to inject an interrupt. I have a
> couple
> of experiments suggestions below.
> 
FWIW, I know that numbers are always relative (hw platform, workload,
etc), and I'm happy to see that you're quite confident that we can
improve further... but these numbers seems rather good to me. :-)

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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