Re: [RFC PATCH v1 2/6] sched: track time spent in hypervisor tasks

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Thu, 2020-09-24 at 18:08 +0000, Volodymyr Babchuk wrote:
> So, as I see this, functions are called in the following way (on
> x86):
> 
> 1. do_softirq() calls vcpu_begin_hyp_task() and then executes
> __do_softirq()
> 
> 2. __do_softirq() does different jobs and eventually calls schedule()
> 
> 3. schedule() calls vcpu_end_hyp_task() and makes scheduling decision
> which leads to call to context_switch()
> 
> 4. On end context_switch() we will exit hypervisor and enter VM. At
> least, this is how I understand
> 
>        nextd->arch.ctxt_switch->tail(next);
> 
> call.
> 
> So, no need to call vcpu_begin_hyp_task() in context_switch() for
> x86.
> 
Mmm... This looks correct to me too.

And what about the cases where schedule() does return?

Are these also fine because they're handled within __do_softirq()
(i.e., without actually going back to do_softirq() and hence never
calling end_hyp_task() for a second time)?


> I have put bunch of ASSERTs to ensure that vcpu_begin_hyp_task() or
> vcpu_end_hyp_task() are not called twice and that vcpu_end_hyp_task()
> is
> called after vcpu_begin_hyp_task(). Those asserts are not failing, so
> I
> assume that I did all this in the right way :)
> 
Yeah, good to know. :-)

Are you doing these tests with both core-scheduling disabled and
enabled?

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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