Re: [patch] sched: fix/add missing update_rq_clock() calls

Ingo Molnar
2009-11-12T11:34:33Z

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, 2009-11-12 at 12:27 +0100, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > > On Thu, 2009-11-12 at 11:07 +0100, Mike Galbraith wrote:
> > > > sched: fix/add missing update_rq_clock() calls.
> > > >
> > > > kthread_bind(), migrate_task() and sched_fork were missing updates, and
> > > > try_to_wake_up() was updating after having already used the stale clock.
> > >
> > >
> > > I'm almost at the point where I think we should ditch rq->clock
> > > alltogether and simply call cpu_clock() directly when we need it. This
> > > trying to optimize and avoid calling it game has brought way too many
> > > head-aches.
> >
> > It's not just about optimization - it's also accounting precision - we
> > want to handle the full act of schedule() at a single timestamp - not a
> > series of timestamps.
> >
> > But ... we can get rid of it if it can be done sanely.
>
> Ah, good point, hard to do for the migration paths though.

yes, migration is always the odd one out anyway, unless the hardware
does cross-CPU-synchronous timestamps.

Ingo