Re: [RFC PATCH v1 1/6] sched: track time spent in IRQ handler

[Julien Grall <julien.grall.oss@xxxxxxxxx>]

On Fri, 12 Jun 2020 at 21:08, Dario Faggioli <dfaggioli@xxxxxxxx> wrote:
>
> On Fri, 2020-06-12 at 13:21 +0100, Julien Grall wrote:
> > On 12/06/2020 12:33, Volodymyr Babchuk wrote:
> > > On Fri, 2020-06-12 at 12:29 +0100, Julien Grall wrote:
> > > > > Basically, this value holds time span between calls to
> > > > > schedule(). This
> > > > > variable gets zeroed out every time scheduler requests for time
> > > > > adjustment value. So, it should not depend on total VM run
> > > > > time.
> > > > This is assuming that the scheduler will be called. With the NULL
> > > > scheduler in place, there is a fair chance this may never be
> > > > called.
> > > >
> >
> Yeah, this is a good point. I mean, I wouldn't be sure about "never",
> as even there, we'd probably have softirqs, tasklets, etc... And I
> still have to look at these patches in more details to figure out
> properly whether they'd help for this.

Unlike x86, Xen doesn't prod another pCPU consistently. :) This was
already discussed in multiple threads in the past (see [1] which not
resolved yet).

So yes, I am pretty confident I can recreate a case where the
scheduling function may never be called on Arm :).

Cheers,

[1] 315740e1-3591-0e11-923a-718e06c36445@xxxxxxx