Re: [PATCH 19/25] sched/vite: Handle nice updates under vtime

Peter Zijlstra
2018-11-26T16:11:32Z

On Mon, Nov 26, 2018 at 04:53:54PM +0100, Frederic Weisbecker wrote:
> > > + irq_work_queue_on(&per_cpu(vtime_set_nice_work, cpu), cpu);
> >
> > What happens if you already had one pending? Do we loose updates?
>
> No, if irq_work is already pending, it doesn't requeue iff the work hasn't
> been executed yet and it's guaranteed it will see the freshest update.
> (you should trust more the code you wrote ;-)

Yeah, I do remember hoq irq_work works. What I was asking was about how
this specific handler deals with 'missing' updates.

Suppose we start with state A, set it to B and raise the IPI, then set
it to C before the interrupt happens.

That means the irq_work handler will see C and never observe B.