[RFC PATCH 2/5] powerpc: Implement broadcast timer interrupt as an IPI message

[Preeti U Murthy]

From: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>

For scalability and performance reasons, we want the broadcast timer
interrupts to be handled as efficiently as possible. Fixed IPI messages
are one of the most efficient mechanisms available - they are faster
than the smp_call_function mechanism because the IPI handlers are fixed
and hence they don't involve costly operations such as adding IPI handlers
to the target CPU's function queue, acquiring locks for synchronization etc.

Luckily we have an unused IPI message slot, so use that to implement
broadcast timer interrupts efficiently.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>
Signed-off-by: Preeti U Murthy <preeti at linux.vnet.ibm.com>
---

 arch/powerpc/include/asm/smp.h          |    3 ++-
 arch/powerpc/kernel/smp.c               |   19 +++++++++++++++----
 arch/powerpc/platforms/cell/interrupt.c |    2 +-
 arch/powerpc/platforms/ps3/smp.c        |    2 +-
 4 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 51bf017..d877b69 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -117,7 +117,7 @@ extern int cpu_to_core_id(int cpu);
  *
  * Make sure this matches openpic_request_IPIs in open_pic.c, or what shows up
  * in /proc/interrupts will be wrong!!! --Troy */
-#define PPC_MSG_UNUSED		0
+#define PPC_MSG_TIMER		0
 #define PPC_MSG_RESCHEDULE      1
 #define PPC_MSG_CALL_FUNC_SINGLE	2
 #define PPC_MSG_DEBUGGER_BREAK  3
@@ -190,6 +190,7 @@ extern struct smp_ops_t *smp_ops;
 
 extern void arch_send_call_function_single_ipi(int cpu);
 extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
+extern void arch_send_tick_broadcast(const struct cpumask *mask);
 
 /* Definitions relative to the secondary CPU spin loop
  * and entry point. Not all of them exist on both 32 and
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index bc41e9f..6a68ca4 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -35,6 +35,7 @@
 #include <asm/ptrace.h>
 #include <linux/atomic.h>
 #include <asm/irq.h>
+#include <asm/hw_irq.h>
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/prom.h>
@@ -111,9 +112,9 @@ int smp_generic_kick_cpu(int nr)
 }
 #endif /* CONFIG_PPC64 */
 
-static irqreturn_t unused_action(int irq, void *data)
+static irqreturn_t timer_action(int irq, void *data)
 {
-	/* This slot is unused and hence available for use, if needed */
+	timer_interrupt();
 	return IRQ_HANDLED;
 }
 
@@ -144,14 +145,14 @@ static irqreturn_t debug_ipi_action(int irq, void *data)
 }
 
 static irq_handler_t smp_ipi_action[] = {
-	[PPC_MSG_UNUSED] =  unused_action, /* Slot available for future use */
+	[PPC_MSG_TIMER] =  timer_action,
 	[PPC_MSG_RESCHEDULE] = reschedule_action,
 	[PPC_MSG_CALL_FUNC_SINGLE] = call_function_single_action,
 	[PPC_MSG_DEBUGGER_BREAK] = debug_ipi_action,
 };
 
 const char *smp_ipi_name[] = {
-	[PPC_MSG_UNUSED] =  "ipi unused",
+	[PPC_MSG_TIMER] =  "ipi timer",
 	[PPC_MSG_RESCHEDULE] = "ipi reschedule",
 	[PPC_MSG_CALL_FUNC_SINGLE] = "ipi call function single",
 	[PPC_MSG_DEBUGGER_BREAK] = "ipi debugger",
@@ -221,6 +222,8 @@ irqreturn_t smp_ipi_demux(void)
 		all = xchg(&info->messages, 0);
 
 #ifdef __BIG_ENDIAN
+		if (all & (1 << (24 - 8 * PPC_MSG_TIMER)))
+			timer_interrupt();
 		if (all & (1 << (24 - 8 * PPC_MSG_RESCHEDULE)))
 			scheduler_ipi();
 		if (all & (1 << (24 - 8 * PPC_MSG_CALL_FUNC_SINGLE)))
@@ -266,6 +269,14 @@ void arch_send_call_function_ipi_mask(const struct cpumask *mask)
 		do_message_pass(cpu, PPC_MSG_CALL_FUNC_SINGLE);
 }
 
+void arch_send_tick_broadcast(const struct cpumask *mask)
+{
+	unsigned int cpu;
+
+	for_each_cpu(cpu, mask)
+		do_message_pass(cpu, PPC_MSG_TIMER);
+}
+
 #if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
 void smp_send_debugger_break(void)
 {
diff --git a/arch/powerpc/platforms/cell/interrupt.c b/arch/powerpc/platforms/cell/interrupt.c
index 28166e4..1359113 100644
--- a/arch/powerpc/platforms/cell/interrupt.c
+++ b/arch/powerpc/platforms/cell/interrupt.c
@@ -213,7 +213,7 @@ static void iic_request_ipi(int msg)
 
 void iic_request_IPIs(void)
 {
-	iic_request_ipi(PPC_MSG_UNUSED);
+	iic_request_ipi(PPC_MSG_TIMER);
 	iic_request_ipi(PPC_MSG_RESCHEDULE);
 	iic_request_ipi(PPC_MSG_CALL_FUNC_SINGLE);
 	iic_request_ipi(PPC_MSG_DEBUGGER_BREAK);
diff --git a/arch/powerpc/platforms/ps3/smp.c b/arch/powerpc/platforms/ps3/smp.c
index 488f069..5cb742a 100644
--- a/arch/powerpc/platforms/ps3/smp.c
+++ b/arch/powerpc/platforms/ps3/smp.c
@@ -74,7 +74,7 @@ static int __init ps3_smp_probe(void)
 		* to index needs to be setup.
 		*/
 
-		BUILD_BUG_ON(PPC_MSG_UNUSED	      != 0);
+		BUILD_BUG_ON(PPC_MSG_TIMER	      != 0);
 		BUILD_BUG_ON(PPC_MSG_RESCHEDULE       != 1);
 		BUILD_BUG_ON(PPC_MSG_CALL_FUNC_SINGLE != 2);
 		BUILD_BUG_ON(PPC_MSG_DEBUGGER_BREAK   != 3);