From: Anton Blanchard <anton@samba.org>

Another decent optimisation found in the ia64 port,
dont take the irq descriptor lock or do the note_interrupt
stuff on PER_CPU irqs (ie IPIs).


---

 arch/ppc64/kernel/irq.c |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff -puN arch/ppc64/kernel/irq.c~ppc64-irq_per_cpu arch/ppc64/kernel/irq.c
--- 25/arch/ppc64/kernel/irq.c~ppc64-irq_per_cpu	2004-02-21 20:58:30.000000000 -0800
+++ 25-akpm/arch/ppc64/kernel/irq.c	2004-02-21 20:58:30.000000000 -0800
@@ -476,8 +476,18 @@ void ppc_irq_dispatch_handler(struct pt_
 	struct irqaction *action;
 	int cpu = smp_processor_id();
 	irq_desc_t *desc = irq_desc + irq;
+	irqreturn_t action_ret;
 
 	kstat_cpu(cpu).irqs[irq]++;
+
+	if (desc->status & IRQ_PER_CPU) {
+		/* no locking required for CPU-local interrupts: */
+		ack_irq(irq);
+		action_ret = handle_irq_event(irq, regs, desc->action);
+		desc->handler->end(irq);
+		return;
+	}
+
 	spin_lock(&desc->lock);
 	ack_irq(irq);	
 	/*
@@ -485,8 +495,7 @@ void ppc_irq_dispatch_handler(struct pt_
 	   WAITING is used by probe to mark irqs that are being tested
 	   */
 	status = desc->status & ~(IRQ_REPLAY | IRQ_WAITING);
-	if (!(status & IRQ_PER_CPU))
-		status |= IRQ_PENDING; /* we _want_ to handle it */
+	status |= IRQ_PENDING; /* we _want_ to handle it */
 
 	/*
 	 * If the IRQ is disabled for whatever reason, we cannot
@@ -509,8 +518,7 @@ void ppc_irq_dispatch_handler(struct pt_
 			goto out;
 		}
 		status &= ~IRQ_PENDING; /* we commit to handling */
-		if (!(status & IRQ_PER_CPU))
-			status |= IRQ_INPROGRESS; /* we are handling it */
+		status |= IRQ_INPROGRESS; /* we are handling it */
 	}
 	desc->status = status;
 
@@ -534,8 +542,6 @@ void ppc_irq_dispatch_handler(struct pt_
 	 * SMP environment.
 	 */
 	for (;;) {
-		irqreturn_t action_ret;
-
 		spin_unlock(&desc->lock);
 		action_ret = handle_irq_event(irq, regs, action);
 		spin_lock(&desc->lock);

_