Re: [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:

quoted

On Fri, 18 Mar 2011, David Daney wrote:

quoted

--- 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 :)
 

quoted

quoted

  #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.

quoted

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