On Tue, Dec 29, 2020 at 02:12:31PM +0000, Qais Yousef wrote:
> On 12/29/20 14:41, Frederic Weisbecker wrote:
> > > > -void vtime_account_irq(struct task_struct *tsk)
> > > > +void vtime_account_irq(struct task_struct *tsk, unsigned int offset)
> > > > {
> > > > - if (hardirq_count()) {
> > > > + unsigned int pc = preempt_count() - offset;
> > > > +
> > > > + if (pc & HARDIRQ_OFFSET) {
> > >
> > > Shouldn't this be HARDIRQ_MASK like above?
> >
> > In the rare cases of nested hardirqs happening with broken drivers, Only
> > the outer hardirq
> > does matter. All the time spent in the inner hardirqs is included in the
> > outer
> > one.
>
> Ah I see. The original code was doing hardirq_count(), which apparently wasn't
> right either.
>
> Shouldn't it be pc == HARDIRQ_OFFSET then? All odd nest counts will trigger
> this otherwise, and IIUC we want this to trigger once on first entry only.
Right but we must also handle hardirqs interrupting either preempt disabled
sections
or softirq servicing/disabled section.
3 stacking hardirqs should be rare enough that we don't really care. In the
worst case we are going to account the third IRQ seperately. Not a correctness
issue, just a rare unoptimized case.
>
> Thanks
>
> --
> Qais Yousef
