On Thu, Nov 21, 2013 at 12:41:44PM +0100, Thomas Gleixner wrote:
> On Wed, 20 Nov 2013, Thomas Gleixner wrote:
> > On Wed, 20 Nov 2013, Tony Luck wrote:
> > > asmlinkage void __sched preempt_schedule_irq(void)
> > > {
> > > schedule();
> > > }
> > >
> > > Or is life more complicated than that?
> >
> > Hmm, I think I fubared that and you decided to ignore my patch :)
> >
> > Let me look at it tomorrow morning with full awake brain cells.
>
> Ok, wrapped my brain around it. I tripped over the magic asm foo which
> has a single need_resched check and schedule point for both sys call
> return and interrupt return.
>
> So you need the schedule_preempt_irq() for kernel preemption from
> interrupt return while on a normal syscall preemption a schedule would
> be sufficient. But using schedule_preempt_irq() is not harmful here in
> any way. It just sets the preempt_active bit also in cases where it
> would not be required.
>
> Even on preempt=n kernels adding the preempt_active bit is completely
> harmless. So instead of having an extra function, moving the existing
> one out of the ifdef PREEMPT looks like the sanest thing to do.
>
> Peter, Ingo ?
So that's because the schedule point is on a common user and kernel return path?
If necessary, why not having a SCHEDULE_IRQ macro in ia64 that maps to either schedule or
preempt_schedule_irq() instead?
Unless that problem happens elsewhere as well?
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