[PATCH] remove multiple IRQ optimisation

[Anton Blanchard]

ppc64 has an optimisation where it loops on get_irq until there are no
more interrupts to be handled. Mark Hack notes that this optimisation
hardly ever hits and costs us a potentially expensive extra read of an
interrupt register every interrupt.

Also make do_IRQ void, the callers never use the return value.

Signed-off-by: Anton Blanchard <anton at samba.org>

===== arch/ppc64/kernel/irq.c 1.62 vs edited =====
--- 1.62/arch/ppc64/kernel/irq.c	Fri Jul  2 15:23:46 2004
+++ edited/arch/ppc64/kernel/irq.c	Fri Jul 16 01:39:54 2004
@@ -589,7 +589,7 @@
 }

 #ifdef CONFIG_PPC_ISERIES
-int do_IRQ(struct pt_regs *regs)
+void do_IRQ(struct pt_regs *regs)
 {
 	struct paca_struct *lpaca;
 	struct ItLpQueue *lpq;
@@ -629,15 +629,13 @@
 		/* Signal a fake decrementer interrupt */
 		timer_interrupt(regs);
 	}
-
-	return 1; /* lets ret_from_int know we can do checks */
 }

 #else	/* CONFIG_PPC_ISERIES */

-int do_IRQ(struct pt_regs *regs)
+void do_IRQ(struct pt_regs *regs)
 {
-	int irq, first = 1;
+	int irq;

 	irq_enter();

@@ -656,25 +654,15 @@
 	}
 #endif

-	/*
-	 * Every arch is required to implement ppc_md.get_irq.
-	 * This function will either return an irq number or -1 to
-	 * indicate there are no more pending.  But the first time
-	 * through the loop this means there wasn't an IRQ pending.
-	 * The value -2 is for buggy hardware and means that this IRQ
-	 * has already been handled. -- Tom
-	 */
-	while ((irq = ppc_md.get_irq(regs)) >= 0) {
+	irq = ppc_md.get_irq(regs);
+
+	if (irq >= 0)
 		ppc_irq_dispatch_handler(regs, irq);
-		first = 0;
-	}
-	if (irq != -2 && first)
+	else
 		/* That's not SMP safe ... but who cares ? */
 		ppc_spurious_interrupts++;

 	irq_exit();
-
-	return 1; /* lets ret_from_int know we can do checks */
 }
 #endif	/* CONFIG_PPC_ISERIES */


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