Re: [Xen-devel] [RFC 2/6] schedule: account true system idle time

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Fri, 2019-07-26 at 13:37 +0300, Andrii Anisov wrote:
> From: Andrii Anisov <andrii_anisov@xxxxxxxx>
> 
> Currently the idle time is being accounted as a idle vcpu runtime.
> This is not entirely correct, because the entity named idle vcpu is
> in fact a hypervisor tasks worker. E.g. some softirqs are processed
> by the idle vcpu.
>
That's all very true, and, as discussed both via mail and in person,
I'm all for it.

About the implementation.

> So lets change idle vcpu time accounting and specify system idle time
> as a idle vcpu blocked time. 
>
This, for one, doesn't really look right to me. You're trying to make
things more clear and more precise... and that's by hiding real idle
time in the idle_vcpu blocked time metric? :-D :-P

Jokes apart, I see how it is rather easy to do something like this, so
I understand it being done like this in an RFC patch, but I don't think
it's correct.

And, on an even more general perspective, the fact that the hypervisor,
when scheduling the idle vcpu, runs softirq, tasklets, etc, it's a
generic concept, not an arch specific one. So, we really should find a
way to implement this in common code, not in arch code.

Maybe, but I'm just thinking out loud, and I need to think more about
this, we can do things the other way round. I.e., we measure the time
that it takes to run softirq and tasklets, and we subtract it from
idle_vcpu runtime?

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

Attachment: signature.asc
Description: This is a digitally signed message part

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel