Re: [PATCH] Updates to Xen hypercall preemption

[Peter Zijlstra]

On Thu, Jun 22, 2023 at 02:05:13PM +0100, Andrew Cooper wrote:
> On 22/06/2023 9:26 am, Peter Zijlstra wrote:
> > On Thu, Jun 22, 2023 at 07:22:53AM +0200, Juergen Gross wrote:
> >
> >> The hypercalls we are talking of are synchronous ones. They are running
> >> in the context of the vcpu doing the call (like a syscall from userland is
> >> running in the process context).
> > (so time actually passes from the guest's pov?)
> 
> Yes.  And in principle it's wired into stolen time.

Hmm, that means that if the scheduler accounts for stolen time (see
update_rq_clock_task(), PARAVIRT_TIME_ACCOUNTING hunk) then it appears
as if no time has passed, which might affect preemption decisions.

Oh well, we'll think about it when it's shown to be a problem I suppose
:-)