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)

1 files changed, 24 insertions, 38 deletions

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 6b4d4d1e343d..4c0e08685705 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -35,14 +35,14 @@
 #include <linux/vt_kern.h>
 #include <linux/workqueue.h>
 #include <linux/kexec.h>
+#include <linux/irq.h>
 
 #include <asm/ptrace.h>
 
 /* Whether we react on sysrq keys or just ignore them */
 int sysrq_enabled = 1;
 
-static void sysrq_handle_loglevel(int key, struct pt_regs *pt_regs,
-                                  struct tty_struct *tty)
+static void sysrq_handle_loglevel(int key, struct tty_struct *tty)
 {
         int i;
         i = key - '0';
@@ -58,8 +58,7 @@ static struct sysrq_key_op sysrq_loglevel_op = {
 };
 
 #ifdef CONFIG_VT
-static void sysrq_handle_SAK(int key, struct pt_regs *pt_regs,
-                             struct tty_struct *tty)
+static void sysrq_handle_SAK(int key, struct tty_struct *tty)
 {
         if (tty)
                 do_SAK(tty);
@@ -76,8 +75,7 @@ static struct sysrq_key_op sysrq_SAK_op = {
 #endif
 
 #ifdef CONFIG_VT
-static void sysrq_handle_unraw(int key, struct pt_regs *pt_regs,
-                               struct tty_struct *tty)
+static void sysrq_handle_unraw(int key, struct tty_struct *tty)
 {
         struct kbd_struct *kbd = &kbd_table[fg_console];
 
@@ -95,10 +93,9 @@ static struct sysrq_key_op sysrq_unraw_op = {
 #endif /* CONFIG_VT */
 
 #ifdef CONFIG_KEXEC
-static void sysrq_handle_crashdump(int key, struct pt_regs *pt_regs,
-                                struct tty_struct *tty)
+static void sysrq_handle_crashdump(int key, struct tty_struct *tty)
 {
-        crash_kexec(pt_regs);
+        crash_kexec(get_irq_regs());
 }
 static struct sysrq_key_op sysrq_crashdump_op = {
         .handler        = sysrq_handle_crashdump,
@@ -110,8 +107,7 @@ static struct sysrq_key_op sysrq_crashdump_op = {
 #define sysrq_crashdump_op (*(struct sysrq_key_op *)0)
 #endif
 
-static void sysrq_handle_reboot(int key, struct pt_regs *pt_regs,
-                                struct tty_struct *tty)
+static void sysrq_handle_reboot(int key, struct tty_struct *tty)
 {
         lockdep_off();
         local_irq_enable();
@@ -124,8 +120,7 @@ static struct sysrq_key_op sysrq_reboot_op = {
         .enable_mask    = SYSRQ_ENABLE_BOOT,
 };
 
-static void sysrq_handle_sync(int key, struct pt_regs *pt_regs,
-                              struct tty_struct *tty)
+static void sysrq_handle_sync(int key, struct tty_struct *tty)
 {
         emergency_sync();
 }
@@ -136,8 +131,7 @@ static struct sysrq_key_op sysrq_sync_op = {
         .enable_mask    = SYSRQ_ENABLE_SYNC,
 };
 
-static void sysrq_handle_mountro(int key, struct pt_regs *pt_regs,
-                                 struct tty_struct *tty)
+static void sysrq_handle_mountro(int key, struct tty_struct *tty)
 {
         emergency_remount();
 }
@@ -149,8 +143,7 @@ static struct sysrq_key_op sysrq_mountro_op = {
 };
 
 #ifdef CONFIG_LOCKDEP
-static void sysrq_handle_showlocks(int key, struct pt_regs *pt_regs,
-                                struct tty_struct *tty)
+static void sysrq_handle_showlocks(int key, struct tty_struct *tty)
 {
         debug_show_all_locks();
 }
@@ -164,11 +157,11 @@ static struct sysrq_key_op sysrq_showlocks_op = {
 #define sysrq_showlocks_op (*(struct sysrq_key_op *)0)
 #endif
 
-static void sysrq_handle_showregs(int key, struct pt_regs *pt_regs,
-                                  struct tty_struct *tty)
+static void sysrq_handle_showregs(int key, struct tty_struct *tty)
 {
-        if (pt_regs)
-                show_regs(pt_regs);
+        struct pt_regs *regs = get_irq_regs();
+        if (regs)
+                show_regs(regs);
 }
 static struct sysrq_key_op sysrq_showregs_op = {
         .handler        = sysrq_handle_showregs,
@@ -177,8 +170,7 @@ static struct sysrq_key_op sysrq_showregs_op = {
         .enable_mask    = SYSRQ_ENABLE_DUMP,
 };
 
-static void sysrq_handle_showstate(int key, struct pt_regs *pt_regs,
-                                   struct tty_struct *tty)
+static void sysrq_handle_showstate(int key, struct tty_struct *tty)
 {
         show_state();
 }
@@ -189,8 +181,7 @@ static struct sysrq_key_op sysrq_showstate_op = {
         .enable_mask    = SYSRQ_ENABLE_DUMP,
 };
 
-static void sysrq_handle_showmem(int key, struct pt_regs *pt_regs,
-                                 struct tty_struct *tty)
+static void sysrq_handle_showmem(int key, struct tty_struct *tty)
 {
         show_mem();
 }
@@ -215,8 +206,7 @@ static void send_sig_all(int sig)
         }
 }
 
-static void sysrq_handle_term(int key, struct pt_regs *pt_regs,
-                              struct tty_struct *tty)
+static void sysrq_handle_term(int key, struct tty_struct *tty)
 {
         send_sig_all(SIGTERM);
         console_loglevel = 8;
@@ -236,8 +226,7 @@ static void moom_callback(void *ignored)
 
 static DECLARE_WORK(moom_work, moom_callback, NULL);
 
-static void sysrq_handle_moom(int key, struct pt_regs *pt_regs,
-                              struct tty_struct *tty)
+static void sysrq_handle_moom(int key, struct tty_struct *tty)
 {
         schedule_work(&moom_work);
 }
@@ -247,8 +236,7 @@ static struct sysrq_key_op sysrq_moom_op = {
         .action_msg     = "Manual OOM execution",
 };
 
-static void sysrq_handle_kill(int key, struct pt_regs *pt_regs,
-                              struct tty_struct *tty)
+static void sysrq_handle_kill(int key, struct tty_struct *tty)
 {
         send_sig_all(SIGKILL);
         console_loglevel = 8;
@@ -260,8 +248,7 @@ static struct sysrq_key_op sysrq_kill_op = {
         .enable_mask    = SYSRQ_ENABLE_SIGNAL,
 };
 
-static void sysrq_handle_unrt(int key, struct pt_regs *pt_regs,
-                                struct tty_struct *tty)
+static void sysrq_handle_unrt(int key, struct tty_struct *tty)
 {
         normalize_rt_tasks();
 }
@@ -361,8 +348,7 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
  * This is the non-locking version of handle_sysrq.  It must/can only be called
  * by sysrq key handlers, as they are inside of the lock
  */
-void __handle_sysrq(int key, struct pt_regs *pt_regs, struct tty_struct *tty,
-                        int check_mask)
+void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
 {
         struct sysrq_key_op *op_p;
         int orig_log_level;
@@ -384,7 +370,7 @@ void __handle_sysrq(int key, struct pt_regs *pt_regs, struct tty_struct *tty,
                     (sysrq_enabled & op_p->enable_mask)) {
                         printk("%s\n", op_p->action_msg);
                         console_loglevel = orig_log_level;
-                        op_p->handler(key, pt_regs, tty);
+                        op_p->handler(key, tty);
                 } else {
                         printk("This sysrq operation is disabled.\n");
                 }
@@ -413,11 +399,11 @@ void __handle_sysrq(int key, struct pt_regs *pt_regs, struct tty_struct *tty,
  * This function is called by the keyboard handler when SysRq is pressed
  * and any other keycode arrives.
  */
-void handle_sysrq(int key, struct pt_regs *pt_regs, struct tty_struct *tty)
+void handle_sysrq(int key, struct tty_struct *tty)
 {
         if (!sysrq_enabled)
                 return;
-        __handle_sysrq(key, pt_regs, tty, 1);
+        __handle_sysrq(key, tty, 1);
 }
 EXPORT_SYMBOL(handle_sysrq);