IRQ: Maintain regs pointer globally rather than passing to IRQ handlers

Maintain a per-CPU global "struct pt_regs *" variable which can be used instead
of passing regs around manually through all ~1800 interrupt handlers in the
Linux kernel.

The regs pointer is used in few places, but it potentially costs both stack
space and code to pass it around.  On the FRV arch, removing the regs parameter
from all the genirq function results in a 20% speed up of the IRQ exit path
(ie: from leaving timer_interrupt() to leaving do_IRQ()).

Where appropriate, an arch may override the generic storage facility and do
something different with the variable.  On FRV, for instance, the address is
maintained in GR28 at all times inside the kernel as part of general exception
handling.

Having looked over the code, it appears that the parameter may be handed down
through up to twenty or so layers of functions.  Consider a USB character
device attached to a USB hub, attached to a USB controller that posts its
interrupts through a cascaded auxiliary interrupt controller.  A character
device driver may want to pass regs to the sysrq handler through the input
layer which adds another few layers of parameter passing.

I've build this code with allyesconfig for x86_64 and i386.  I've runtested the
main part of the code on FRV and i386, though I can't test most of the drivers.
I've also done partial conversion for powerpc and MIPS - these at least compile
with minimal configurations.

This will affect all archs.  Mostly the changes should be relatively easy.
Take do_IRQ(), store the regs pointer at the beginning, saving the old one:

	struct pt_regs *old_regs = set_irq_regs(regs);

And put the old one back at the end:

	set_irq_regs(old_regs);

Don't pass regs through to generic_handle_irq() or __do_IRQ().

In timer_interrupt(), this sort of change will be necessary:

	-	update_process_times(user_mode(regs));
	-	profile_tick(CPU_PROFILING, regs);
	+	update_process_times(user_mode(get_irq_regs()));
	+	profile_tick(CPU_PROFILING);

I'd like to move update_process_times()'s use of get_irq_regs() into itself,
except that i386, alone of the archs, uses something other than user_mode().

Some notes on the interrupt handling in the drivers:

 (*) input_dev() is now gone entirely.  The regs pointer is no longer stored in
     the input_dev struct.

 (*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking.  It does
     something different depending on whether it's been supplied with a regs
     pointer or not.

 (*) Various IRQ handler function pointers have been moved to type
     irq_handler_t.

Signed-Off-By: David Howells <dhowells@redhat.com>
(cherry picked from 1b16e7ac850969f38b375e511e3fa2f474a33867 commit)

4 files changed, 15 insertions, 9 deletions

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index c3f58f2..5deaab3 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -187,6 +187,7 @@ void fixup_irqs(cpumask_t map)
 
 void do_IRQ(struct pt_regs *regs)
 {
+	struct pt_regs *old_regs = set_irq_regs(regs);
 	unsigned int irq;
 #ifdef CONFIG_IRQSTACKS
 	struct thread_info *curtp, *irqtp;
@@ -230,18 +231,19 @@ void do_IRQ(struct pt_regs *regs)
 				handler = &__do_IRQ;
 			irqtp->task = curtp->task;
 			irqtp->flags = 0;
-			call_handle_irq(irq, desc, regs, irqtp, handler);
+			call_handle_irq(irq, desc, irqtp, handler);
 			irqtp->task = NULL;
 			if (irqtp->flags)
 				set_bits(irqtp->flags, &curtp->flags);
 		} else
 #endif
-			generic_handle_irq(irq, regs);
+			generic_handle_irq(irq);
 	} else if (irq != NO_IRQ_IGNORE)
 		/* That's not SMP safe ... but who cares ? */
 		ppc_spurious_interrupts++;
 
         irq_exit();
+	set_irq_regs(old_regs);
 
 #ifdef CONFIG_PPC_ISERIES
 	if (get_lppaca()->int_dword.fields.decr_int) {
diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
index 41521b3..c70e207 100644
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -52,12 +52,12 @@ _GLOBAL(call_do_softirq)
 	blr
 
 _GLOBAL(call_handle_irq)
-	ld	r8,0(r7)
+	ld	r8,0(r6)
 	mflr	r0
 	std	r0,16(r1)
 	mtctr	r8
-	stdu	r1,THREAD_SIZE-112(r6)
-	mr	r1,r6
+	stdu	r1,THREAD_SIZE-112(r5)
+	mr	r1,r5
 	bctrl
 	ld	r1,0(r1)
 	ld	r0,16(r1)
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 6a9bc9c..35c6309 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -115,7 +115,7 @@ void __devinit smp_generic_kick_cpu(int nr)
 }
 #endif
 
-void smp_message_recv(int msg, struct pt_regs *regs)
+void smp_message_recv(int msg)
 {
 	switch(msg) {
 	case PPC_MSG_CALL_FUNCTION:
@@ -127,11 +127,11 @@ void smp_message_recv(int msg, struct pt_regs *regs)
 		break;
 	case PPC_MSG_DEBUGGER_BREAK:
 		if (crash_ipi_function_ptr) {
-			crash_ipi_function_ptr(regs);
+			crash_ipi_function_ptr(get_irq_regs());
 			break;
 		}
 #ifdef CONFIG_DEBUGGER
-		debugger_ipi(regs);
+		debugger_ipi(get_irq_regs());
 		break;
 #endif /* CONFIG_DEBUGGER */
 		/* FALLTHROUGH */
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 85b9244..d210d0a 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -51,6 +51,7 @@
 #include <linux/rtc.h>
 #include <linux/jiffies.h>
 #include <linux/posix-timers.h>
+#include <linux/irq.h>
 
 #include <asm/io.h>
 #include <asm/processor.h>
@@ -643,6 +644,7 @@ static void iSeries_tb_recal(void)
  */
 void timer_interrupt(struct pt_regs * regs)
 {
+	struct pt_regs *old_regs;
 	int next_dec;
 	int cpu = smp_processor_id();
 	unsigned long ticks;
@@ -653,9 +655,10 @@ void timer_interrupt(struct pt_regs * regs)
 		do_IRQ(regs);
 #endif
 
+	old_regs = set_irq_regs(regs);
 	irq_enter();
 
-	profile_tick(CPU_PROFILING, regs);
+	profile_tick(CPU_PROFILING);
 	calculate_steal_time();
 
 #ifdef CONFIG_PPC_ISERIES
@@ -715,6 +718,7 @@ void timer_interrupt(struct pt_regs * regs)
 #endif
 
 	irq_exit();
+	set_irq_regs(old_regs);
 }
 
 void wakeup_decrementer(void)