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)

7 files changed, 31 insertions, 21 deletions

diff --git a/arch/i386/kernel/apic.c b/arch/i386/kernel/apic.c
index 90faae5c5d30..7d500da0e63b 100644
--- a/arch/i386/kernel/apic.c
+++ b/arch/i386/kernel/apic.c
@@ -1193,11 +1193,11 @@ EXPORT_SYMBOL(switch_ipi_to_APIC_timer);
  * value into /proc/profile.
  */
 
-inline void smp_local_timer_interrupt(struct pt_regs * regs)
+inline void smp_local_timer_interrupt(void)
 {
-        profile_tick(CPU_PROFILING, regs);
+        profile_tick(CPU_PROFILING);
 #ifdef CONFIG_SMP
-        update_process_times(user_mode_vm(regs));
+        update_process_times(user_mode_vm(irq_regs));
 #endif
 
         /*
@@ -1223,6 +1223,7 @@ inline void smp_local_timer_interrupt(struct pt_regs * regs)
 
 fastcall void smp_apic_timer_interrupt(struct pt_regs *regs)
 {
+        struct pt_regs *old_regs = set_irq_regs(regs);
         int cpu = smp_processor_id();
 
         /*
@@ -1241,12 +1242,13 @@ fastcall void smp_apic_timer_interrupt(struct pt_regs *regs)
          * interrupt lock, which is the WrongThing (tm) to do.
          */
         irq_enter();
-        smp_local_timer_interrupt(regs);
+        smp_local_timer_interrupt();
         irq_exit();
+        set_irq_regs(old_regs);
 }
 
 #ifndef CONFIG_SMP
-static void up_apic_timer_interrupt_call(struct pt_regs *regs)
+static void up_apic_timer_interrupt_call(void)
 {
         int cpu = smp_processor_id();
 
@@ -1255,11 +1257,11 @@ static void up_apic_timer_interrupt_call(struct pt_regs *regs)
          */
         per_cpu(irq_stat, cpu).apic_timer_irqs++;
 
-        smp_local_timer_interrupt(regs);
+        smp_local_timer_interrupt();
 }
 #endif
 
-void smp_send_timer_broadcast_ipi(struct pt_regs *regs)
+void smp_send_timer_broadcast_ipi(void)
 {
         cpumask_t mask;
 
@@ -1272,7 +1274,7 @@ void smp_send_timer_broadcast_ipi(struct pt_regs *regs)
                  * We can directly call the apic timer interrupt handler
                  * in UP case. Minus all irq related functions
                  */
-                up_apic_timer_interrupt_call(regs);
+                up_apic_timer_interrupt_call();
 #endif
         }
 }
diff --git a/arch/i386/kernel/i8259.c b/arch/i386/kernel/i8259.c
index d07ed31f11e3..d53eafb6daa7 100644
--- a/arch/i386/kernel/i8259.c
+++ b/arch/i386/kernel/i8259.c
@@ -335,13 +335,13 @@ void init_8259A(int auto_eoi)
  */
  
 
-static irqreturn_t math_error_irq(int cpl, void *dev_id, struct pt_regs *regs)
+static irqreturn_t math_error_irq(int cpl, void *dev_id)
 {
         extern void math_error(void __user *);
         outb(0,0xF0);
         if (ignore_fpu_irq || !boot_cpu_data.hard_math)
                 return IRQ_NONE;
-        math_error((void __user *)regs->eip);
+        math_error((void __user *)get_irq_regs()->eip);
         return IRQ_HANDLED;
 }
 
diff --git a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
index 3dd2e180151b..8cfc7dbec7b9 100644
--- a/arch/i386/kernel/irq.c
+++ b/arch/i386/kernel/irq.c
@@ -53,6 +53,7 @@ static union irq_ctx *softirq_ctx[NR_CPUS] __read_mostly;
  */
 fastcall unsigned int do_IRQ(struct pt_regs *regs)
 {       
+        struct pt_regs *old_regs;
         /* high bit used in ret_from_ code */
         int irq = ~regs->orig_eax;
         struct irq_desc *desc = irq_desc + irq;
@@ -67,6 +68,7 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
                 BUG();
         }
 
+        old_regs = set_irq_regs(regs);
         irq_enter();
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
         /* Debugging check for stack overflow: is there less than 1KB free? */
@@ -95,7 +97,7 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
          * current stack (which is the irq stack already after all)
          */
         if (curctx != irqctx) {
-                int arg1, arg2, arg3, ebx;
+                int arg1, arg2, ebx;
 
                 /* build the stack frame on the IRQ stack */
                 isp = (u32*) ((char*)irqctx + sizeof(*irqctx));
@@ -114,17 +116,17 @@ fastcall unsigned int do_IRQ(struct pt_regs *regs)
                         "       xchgl  %%ebx,%%esp      \n"
                         "       call   *%%edi           \n"
                         "       movl   %%ebx,%%esp      \n"
-                        : "=a" (arg1), "=d" (arg2), "=c" (arg3), "=b" (ebx)
-                        :  "0" (irq),   "1" (desc),  "2" (regs),  "3" (isp),
+                        : "=a" (arg1), "=d" (arg2), "=b" (ebx)
+                        :  "0" (irq),   "1" (desc),  "2" (isp),
                            "D" (desc->handle_irq)
                         : "memory", "cc"
                 );
         } else
 #endif
-                desc->handle_irq(irq, desc, regs);
+                desc->handle_irq(irq, desc);
 
         irq_exit();
-
+        set_irq_regs(old_regs);
         return 1;
 }
 
diff --git a/arch/i386/kernel/smp.c b/arch/i386/kernel/smp.c
index 1b080ab8a49f..31e5c6573aae 100644
--- a/arch/i386/kernel/smp.c
+++ b/arch/i386/kernel/smp.c
@@ -321,6 +321,7 @@ static inline void leave_mm (unsigned long cpu)
 
 fastcall void smp_invalidate_interrupt(struct pt_regs *regs)
 {
+        struct pt_regs *old_regs = set_irq_regs(regs);
         unsigned long cpu;
 
         cpu = get_cpu();
@@ -351,6 +352,7 @@ fastcall void smp_invalidate_interrupt(struct pt_regs *regs)
         smp_mb__after_clear_bit();
 out:
         put_cpu_no_resched();
+        set_irq_regs(old_regs);
 }
 
 static void flush_tlb_others(cpumask_t cpumask, struct mm_struct *mm,
@@ -605,11 +607,14 @@ void smp_send_stop(void)
  */
 fastcall void smp_reschedule_interrupt(struct pt_regs *regs)
 {
+        struct pt_regs *old_regs = set_irq_regs(regs);
         ack_APIC_irq();
+        set_irq_regs(old_regs);
 }
 
 fastcall void smp_call_function_interrupt(struct pt_regs *regs)
 {
+        struct pt_regs *old_regs = set_irq_regs(regs);
         void (*func) (void *info) = call_data->func;
         void *info = call_data->info;
         int wait = call_data->wait;
@@ -632,6 +637,7 @@ fastcall void smp_call_function_interrupt(struct pt_regs *regs)
                 mb();
                 atomic_inc(&call_data->finished);
         }
+        set_irq_regs(old_regs);
 }
 
 /*
diff --git a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
index 58a2d5582419..3f221f5eb47e 100644
--- a/arch/i386/kernel/time.c
+++ b/arch/i386/kernel/time.c
@@ -161,7 +161,7 @@ EXPORT_SYMBOL(profile_pc);
  * Time Stamp Counter value at the time of the timer interrupt, so that
  * we later on can estimate the time of day more exactly.
  */
-irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+irqreturn_t timer_interrupt(int irq, void *dev_id)
 {
         /*
          * Here we are in the timer irq handler. We just have irqs locally
@@ -188,7 +188,7 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
         }
 #endif
 
-        do_timer_interrupt_hook(regs);
+        do_timer_interrupt_hook();
 
 
         if (MCA_bus) {
@@ -209,7 +209,7 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 
 #ifdef CONFIG_X86_LOCAL_APIC
         if (using_apic_timer)
-                smp_send_timer_broadcast_ipi(regs);
+                smp_send_timer_broadcast_ipi();
 #endif
 
         return IRQ_HANDLED;
diff --git a/arch/i386/kernel/time_hpet.c b/arch/i386/kernel/time_hpet.c
index 6bf14a4e995e..1a2a979cf6a3 100644
--- a/arch/i386/kernel/time_hpet.c
+++ b/arch/i386/kernel/time_hpet.c
@@ -441,7 +441,7 @@ int hpet_rtc_dropped_irq(void)
         return 1;
 }
 
-irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
 {
         struct rtc_time curr_time;
         unsigned long rtc_int_flag = 0;
@@ -480,7 +480,7 @@ 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;
 }
diff --git a/arch/i386/kernel/vm86.c b/arch/i386/kernel/vm86.c
index 8355d8d87d18..cbcd61d6120b 100644
--- a/arch/i386/kernel/vm86.c
+++ b/arch/i386/kernel/vm86.c
@@ -714,7 +714,7 @@ static int irqbits;
         | (1 << SIGUSR1) | (1 << SIGUSR2) | (1 << SIGIO)  | (1 << SIGURG) \
         | (1 << SIGUNUSED) )
         
-static irqreturn_t irq_handler(int intno, void *dev_id, struct pt_regs * regs)
+static irqreturn_t irq_handler(int intno, void *dev_id)
 {
         int irq_bit;
         unsigned long flags;