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)

3 files changed, 21 insertions, 18 deletions

diff --git a/arch/x86_64/kernel/apic.c b/arch/x86_64/kernel/apic.c
index 6472e32..af4a1c7 100644
--- a/arch/x86_64/kernel/apic.c
+++ b/arch/x86_64/kernel/apic.c
@@ -885,14 +885,14 @@ void setup_APIC_extened_lvt(unsigned char lvt_off, unsigned char vector,
  * value into /proc/profile.
  */
 
-void smp_local_timer_interrupt(struct pt_regs *regs)
+void smp_local_timer_interrupt(void)
 {
-	profile_tick(CPU_PROFILING, regs);
+	profile_tick(CPU_PROFILING);
 #ifdef CONFIG_SMP
-	update_process_times(user_mode(regs));
+	update_process_times(user_mode(get_irq_regs()));
 #endif
 	if (apic_runs_main_timer > 1 && smp_processor_id() == boot_cpu_id)
-		main_timer_handler(regs);
+		main_timer_handler();
 	/*
 	 * We take the 'long' return path, and there every subsystem
 	 * grabs the appropriate locks (kernel lock/ irq lock).
@@ -913,7 +913,7 @@ void smp_local_timer_interrupt(struct pt_regs *regs)
  * [ if a single-CPU system runs an SMP kernel then we call the local
  *   interrupt as well. Thus we cannot inline the local irq ... ]
  */
-void smp_apic_timer_interrupt(struct pt_regs *regs)
+void smp_apic_timer_interrupt(void)
 {
 	/*
 	 * the NMI deadlock-detector uses this.
@@ -932,7 +932,7 @@ void smp_apic_timer_interrupt(struct pt_regs *regs)
 	 */
 	exit_idle();
 	irq_enter();
-	smp_local_timer_interrupt(regs);
+	smp_local_timer_interrupt();
 	irq_exit();
 }
 
diff --git a/arch/x86_64/kernel/irq.c b/arch/x86_64/kernel/irq.c
index 506f27c..b8a407f 100644
--- a/arch/x86_64/kernel/irq.c
+++ b/arch/x86_64/kernel/irq.c
@@ -103,7 +103,9 @@ skip:
  * handlers).
  */
 asmlinkage unsigned int do_IRQ(struct pt_regs *regs)
-{	
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+
 	/* high bit used in ret_from_ code  */
 	unsigned vector = ~regs->orig_rax;
 	unsigned irq;
@@ -121,9 +123,10 @@ asmlinkage unsigned int do_IRQ(struct pt_regs *regs)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 	stack_overflow_check(regs);
 #endif
-	generic_handle_irq(irq, regs);
+	generic_handle_irq(irq);
 	irq_exit();
 
+	set_irq_regs(old_regs);
 	return 1;
 }
 
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 557e92a..1ba5a44 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -302,20 +302,20 @@ unsigned long long monotonic_clock(void)
 }
 EXPORT_SYMBOL(monotonic_clock);
 
-static noinline void handle_lost_ticks(int lost, struct pt_regs *regs)
+static noinline void handle_lost_ticks(int lost)
 {
 	static long lost_count;
 	static int warned;
 	if (report_lost_ticks) {
 		printk(KERN_WARNING "time.c: Lost %d timer tick(s)! ", lost);
-		print_symbol("rip %s)\n", regs->rip);
+		print_symbol("rip %s)\n", get_irq_regs()->rip);
 	}
 
 	if (lost_count == 1000 && !warned) {
 		printk(KERN_WARNING "warning: many lost ticks.\n"
 		       KERN_WARNING "Your time source seems to be instable or "
 		   		"some driver is hogging interupts\n");
-		print_symbol("rip %s\n", regs->rip);
+		print_symbol("rip %s\n", get_irq_regs()->rip);
 		if (vxtime.mode == VXTIME_TSC && vxtime.hpet_address) {
 			printk(KERN_WARNING "Falling back to HPET\n");
 			if (hpet_use_timer)
@@ -339,7 +339,7 @@ static noinline void handle_lost_ticks(int lost, struct pt_regs *regs)
 #endif
 }
 
-void main_timer_handler(struct pt_regs *regs)
+void main_timer_handler(void)
 {
 	static unsigned long rtc_update = 0;
 	unsigned long tsc;
@@ -411,7 +411,7 @@ void main_timer_handler(struct pt_regs *regs)
 	}
 
 	if (lost > 0)
-		handle_lost_ticks(lost, regs);
+		handle_lost_ticks(lost);
 	else
 		lost = 0;
 
@@ -421,7 +421,7 @@ void main_timer_handler(struct pt_regs *regs)
 
 	do_timer(lost + 1);
 #ifndef CONFIG_SMP
-	update_process_times(user_mode(regs));
+	update_process_times(user_mode(get_irq_regs()));
 #endif
 
 /*
@@ -431,7 +431,7 @@ void main_timer_handler(struct pt_regs *regs)
  */
 
 	if (!using_apic_timer)
-		smp_local_timer_interrupt(regs);
+		smp_local_timer_interrupt();
 
 /*
  * If we have an externally synchronized Linux clock, then update CMOS clock
@@ -450,11 +450,11 @@ void main_timer_handler(struct pt_regs *regs)
 	write_sequnlock(&xtime_lock);
 }
 
-static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t timer_interrupt(int irq, void *dev_id)
 {
 	if (apic_runs_main_timer > 1)
 		return IRQ_HANDLED;
-	main_timer_handler(regs);
+	main_timer_handler();
 	if (using_apic_timer)
 		smp_send_timer_broadcast_ipi();
 	return IRQ_HANDLED;
@@ -1337,7 +1337,7 @@ irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 	}
 	if (call_rtc_interrupt) {
 		rtc_int_flag |= (RTC_IRQF | (RTC_NUM_INTS << 8));
-		rtc_interrupt(rtc_int_flag, dev_id, regs);
+		rtc_interrupt(rtc_int_flag, dev_id);
 	}
 	return IRQ_HANDLED;
 }