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SubjectRe: [RFC PATCH 1/2] genirq: Add chip hooks for taking CPUs on/off line.
On Mon, 21 Mar 2011, David Daney wrote:

> On 03/19/2011 01:51 PM, Thomas Gleixner wrote:
> > On Fri, 18 Mar 2011, David Daney wrote:
> > > --- a/include/linux/irqdesc.h
> > > +++ b/include/linux/irqdesc.h
> > > @@ -178,6 +178,12 @@ static inline int irq_has_action(unsigned int irq)
> > > return desc->action != NULL;
> > > }
> > >
> > > +/* Test to see if the irq is currently enabled */
> > > +static inline int irq_desc_is_enabled(struct irq_desc *desc)
> > > +{
> > > + return desc->depth == 0;
> > > +}
> >
> > That want's to go into kernel/irq/internal.h
>
> I think I need to use this in my irq_chip.irq_unmask method.
>
> Consider this:
>
>
> CPU0 CPU1
> handle_level_irq
> lock
> mask
> handle_irq_event
> unlock
> .
> . disable_irq
> .
> lock
> unmask
> unlock

handle level irq does:

if (!(desc->istate & (IRQS_DISABLED | IRQS_ONESHOT)))
unmask_irq(desc);

So it does not call unmask.

> I need to know in my .unmask method if the interrupt has been disabled. If it
> has, I will not re-enable (unmask)it.

It wont be called :)

> >
> > > #ifndef CONFIG_GENERIC_HARDIRQS_NO_COMPAT
> > > static inline int irq_balancing_disabled(unsigned int irq)
> > > {
> > > diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> > > index c9c0601..40736f7 100644
> > > --- a/kernel/irq/chip.c
> > > +++ b/kernel/irq/chip.c
> > > @@ -689,3 +689,38 @@ void irq_modify_status(unsigned int irq, unsigned
> > > long clr, unsigned long set)
> > >
> > > irq_put_desc_unlock(desc, flags);
> > > }
> > > +
> > > +void irq_cpu_online(unsigned int irq)
> >
> > Odd function name. It does not reflect that this is for per cpu
> > interrupts. So something like irq_xxx_per_cpu_irq(irq)
> > might be a bit more descriptive.
>
> I am using it for per cpu interrupts, but I didn't want to impose that policy
> on others.

I can't imagine any other purpose for that.

> > Though one question remains: should we just iterate over the irq space
> > and call the online/offline callbacks when available instead of having
> > the arch code do the iteration.
> >
>
> That would be good I think, especially for sparse irqs.
>
> In the case of the CPU going offline, the .irq_cpu_offline() may need to
> adjust the affinity so that the irq no longer has affinity for the off-lined
> CPU.
>
> This is something needed even for non-per-cpu interrupts. Also I would need a
> way to call irq_set_affinity() while holding the desc->lock.

Hmm. The offline fixup_irq() code is arch specific and usually calls
desc->irq_data.chip->irq_set_affinity under desc->lock. I have not yet
found an arch independent way to do that. Any ideas welcome.
Thanks,

tglx




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