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

[Julien Grall <julien@xxxxxxx>]

On 12/06/2020 12:26, Volodymyr Babchuk wrote:
> Hi Jurgen,
>
> thanks for the review
>
> On Fri, 2020-06-12 at 06:36 +0200, Jürgen Groß wrote:
>
> > On 12.06.20 02:22, Volodymyr Babchuk wrote:
> [...]
>
> > > +void vcpu_end_irq_handler(void)
> > > +{
> > > +    int delta;
> > > +
> > > +    if (is_idle_vcpu(current))
> > > +        return;
> > > +
> > > +    ASSERT(current->irq_nesting);
> > > +
> > > +    if ( --current->irq_nesting )
> > > +        return;
> > > +
> > > +    /* We assume that irq handling time will not overflow int */
> > This assumption might not hold for long running VMs.
> 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.
So I think using a 64-bit value is likely safer.

Cheers,

--
Julien Grall