Subject: Re: [PATCH] 2.6.18-rt7: PowerPC: fix breakage in threaded fasteoi type IRQ handlers

From: Ingo Molnar <[email-masked]>
Date: Mon, 20 Nov 2006 18:55:02 +0100

* Ingo Molnar <[email-masked]> wrote:

> i'm hacking up something now to see whether it makes sense to 
> introduce a central threaded flow type, or whether it's better the 
> branch off the current flow types (as the code does it right now).

ok, a central flow type caused more problems than good - the main 
complication is that the handler needs to know the true 'flow' 
(edge/level/fasteoi, etc.) anyway, even in the threaded case.

So i rather went on making the existing flow handlers more 
threading-friendly, and undoing the x86_64 and i386 arch changes to make 
sure that the default handlers all work fine. Does the patch below 
(against -rt4) do the trick for your on PPC too?

[ also, i excluded old-style do_IRQ() platforms from irq threading -
  those hopelessly mix all the flow types that makes robust threading
  support not really possible. ]

	Ingo

Index: linux/arch/i386/kernel/io_apic.c
===================================================================
--- linux.orig/arch/i386/kernel/io_apic.c
+++ linux/arch/i386/kernel/io_apic.c
@@ -1272,22 +1272,12 @@ static struct irq_chip ioapic_chip;
 static void ioapic_register_intr(int irq, int vector, unsigned long trigger)
 {
 	if ((trigger == IOAPIC_AUTO && IO_APIC_irq_trigger(irq)) ||
-			trigger == IOAPIC_LEVEL) {
-#ifdef CONFIG_PREEMPT_HARDIRQS
+			trigger == IOAPIC_LEVEL)
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
-					    handle_level_irq, "level-threaded");
-#else
-		set_irq_chip_and_handler_name(irq, &ioapic_chip,
-					      handle_fasteoi_irq, "fasteoi");
-#endif
-	} else {
-#ifdef CONFIG_PREEMPT_HARDIRQS
+					 handle_fasteoi_irq, "fasteoi");
+	else {
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
-					      handle_edge_irq, "edge-threaded");
-#else
-		set_irq_chip_and_handler_name(irq, &ioapic_chip,
-					      handle_edge_irq, "edge");
-#endif
+					 handle_edge_irq, "edge");
 	}
 	set_intr_gate(vector, interrupt[irq]);
 }
Index: linux/arch/x86_64/kernel/io_apic.c
===================================================================
--- linux.orig/arch/x86_64/kernel/io_apic.c
+++ linux/arch/x86_64/kernel/io_apic.c
@@ -787,22 +787,12 @@ static struct irq_chip ioapic_chip;
 static void ioapic_register_intr(int irq, int vector, unsigned long trigger)
 {
 	if ((trigger == IOAPIC_AUTO && IO_APIC_irq_trigger(irq)) ||
-			trigger == IOAPIC_LEVEL) {
-#ifdef CONFIG_PREEMPT_HARDIRQS
-		set_irq_chip_and_handler_name(irq, &ioapic_chip,
-					    handle_level_irq, "level-threaded");
-#else
+			trigger == IOAPIC_LEVEL)
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
 					      handle_fasteoi_irq, "fasteoi");
-#endif
-	} else {
-#ifdef CONFIG_PREEMPT_HARDIRQS
-		set_irq_chip_and_handler_name(irq, &ioapic_chip,
-					      handle_edge_irq, "edge-threaded");
-#else
+	else {
 		set_irq_chip_and_handler_name(irq, &ioapic_chip,
 					      handle_edge_irq, "edge");
-#endif
 	}
 }
 
Index: linux/kernel/Kconfig.preempt
===================================================================
--- linux.orig/kernel/Kconfig.preempt
+++ linux/kernel/Kconfig.preempt
@@ -105,7 +105,7 @@ config PREEMPT_SOFTIRQS
 config PREEMPT_HARDIRQS
 	bool "Thread Hardirqs"
 	default n
-#	depends on PREEMPT
+	depends on !GENERIC_HARDIRQS_NO__DO_IRQ
 	help
 	  This option reduces the latency of the kernel by 'threading'
           hardirqs. This means that all (or selected) hardirqs will run
Index: linux/kernel/irq/chip.c
===================================================================
--- linux.orig/kernel/irq/chip.c
+++ linux/kernel/irq/chip.c
@@ -238,8 +238,10 @@ static inline void mask_ack_irq(struct i
 	if (desc->chip->mask_ack)
 		desc->chip->mask_ack(irq);
 	else {
-		desc->chip->mask(irq);
-		desc->chip->ack(irq);
+		if (desc->chip->mask)
+			desc->chip->mask(irq);
+		if (desc->chip->mask)
+			desc->chip->ack(irq);
 	}
 }
 
Index: linux/kernel/irq/handle.c
===================================================================
--- linux.orig/kernel/irq/handle.c
+++ linux/kernel/irq/handle.c
@@ -266,12 +266,6 @@ fastcall notrace unsigned int __do_IRQ(u
 		goto out;
 
 	/*
-	 * hardirq redirection to the irqd process context:
-	 */
-	if (redirect_hardirq(desc))
-		goto out_no_end;
-
-	/*
 	 * Edge triggered interrupts need to remember
 	 * pending events.
 	 * This applies to any hw interrupts that allow a second
@@ -303,7 +297,6 @@ out:
 	 * disabled while the handler was running.
 	 */
 	desc->chip->end(irq);
-out_no_end:
 	spin_unlock(&desc->lock);
 
 	return 1;