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, 11 insertions, 11 deletions

diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index 280b114e253f..a06d8d1aaceb 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -119,9 +119,9 @@ struct sk_buff *gfar_new_skb(struct net_device *dev, struct rxbd8 *bdp);
 static struct net_device_stats *gfar_get_stats(struct net_device *dev);
 static int gfar_set_mac_address(struct net_device *dev);
 static int gfar_change_mtu(struct net_device *dev, int new_mtu);
-static irqreturn_t gfar_error(int irq, void *dev_id, struct pt_regs *regs);
-static irqreturn_t gfar_transmit(int irq, void *dev_id, struct pt_regs *regs);
-static irqreturn_t gfar_interrupt(int irq, void *dev_id, struct pt_regs *regs);
+static irqreturn_t gfar_error(int irq, void *dev_id);
+static irqreturn_t gfar_transmit(int irq, void *dev_id);
+static irqreturn_t gfar_interrupt(int irq, void *dev_id);
 static void adjust_link(struct net_device *dev);
 static void init_registers(struct net_device *dev);
 static int init_phy(struct net_device *dev);
@@ -1173,7 +1173,7 @@ static void gfar_timeout(struct net_device *dev)
 }
 
 /* Interrupt Handler for Transmit complete */
-static irqreturn_t gfar_transmit(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t gfar_transmit(int irq, void *dev_id)
 {
 	struct net_device *dev = (struct net_device *) dev_id;
 	struct gfar_private *priv = netdev_priv(dev);
@@ -1305,7 +1305,7 @@ static inline void count_errors(unsigned short status, struct gfar_private *priv
 	}
 }
 
-irqreturn_t gfar_receive(int irq, void *dev_id, struct pt_regs *regs)
+irqreturn_t gfar_receive(int irq, void *dev_id)
 {
 	struct net_device *dev = (struct net_device *) dev_id;
 	struct gfar_private *priv = netdev_priv(dev);
@@ -1537,7 +1537,7 @@ static int gfar_poll(struct net_device *dev, int *budget)
 #endif
 
 /* The interrupt handler for devices with one interrupt */
-static irqreturn_t gfar_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t gfar_interrupt(int irq, void *dev_id)
 {
 	struct net_device *dev = dev_id;
 	struct gfar_private *priv = netdev_priv(dev);
@@ -1550,11 +1550,11 @@ static irqreturn_t gfar_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 
 	/* Check for reception */
 	if ((events & IEVENT_RXF0) || (events & IEVENT_RXB0))
-		gfar_receive(irq, dev_id, regs);
+		gfar_receive(irq, dev_id);
 
 	/* Check for transmit completion */
 	if ((events & IEVENT_TXF) || (events & IEVENT_TXB))
-		gfar_transmit(irq, dev_id, regs);
+		gfar_transmit(irq, dev_id);
 
 	/* Update error statistics */
 	if (events & IEVENT_TXE) {
@@ -1578,7 +1578,7 @@ static irqreturn_t gfar_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 		priv->stats.rx_errors++;
 		priv->extra_stats.rx_bsy++;
 
-		gfar_receive(irq, dev_id, regs);
+		gfar_receive(irq, dev_id);
 
 #ifndef CONFIG_GFAR_NAPI
 		/* Clear the halt bit in RSTAT */
@@ -1857,7 +1857,7 @@ static void gfar_set_mac_for_addr(struct net_device *dev, int num, u8 *addr)
 }
 
 /* GFAR error interrupt handler */
-static irqreturn_t gfar_error(int irq, void *dev_id, struct pt_regs *regs)
+static irqreturn_t gfar_error(int irq, void *dev_id)
 {
 	struct net_device *dev = dev_id;
 	struct gfar_private *priv = netdev_priv(dev);
@@ -1898,7 +1898,7 @@ static irqreturn_t gfar_error(int irq, void *dev_id, struct pt_regs *regs)
 		priv->stats.rx_errors++;
 		priv->extra_stats.rx_bsy++;
 
-		gfar_receive(irq, dev_id, regs);
+		gfar_receive(irq, dev_id);
 
 #ifndef CONFIG_GFAR_NAPI
 		/* Clear the halt bit in RSTAT */