Commit 1b67bee1 authored by Srivatsa S. Bhat's avatar Srivatsa S. Bhat Committed by Benjamin Herrenschmidt
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powerpc: Implement tick broadcast IPI as a fixed IPI message 



For scalability and performance reasons, we want the tick broadcast IPIs
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
tick broadcast IPIs efficiently.

Signed-off-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
[Functions renamed to tick_broadcast* and Changelog modified by
 Preeti U. Murthy<preeti@linux.vnet.ibm.com>]
Signed-off-by: default avatarPreeti U. Murthy <preeti@linux.vnet.ibm.com>
Acked-by: Geoff Levand <geoff@infradead.org> [For the PS3 part]
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 402d9a1e

arch/powerpc/include/asm/smp.h

+1 −1
Original line number Diff line number Diff line
@@ -120,7 +120,7 @@ extern int cpu_to_core_id(int cpu); 
 * in /proc/interrupts will be wrong!!! --Troy */

#define PPC_MSG_CALL_FUNCTION   0

#define PPC_MSG_RESCHEDULE      1

#define PPC_MSG_UNUSED		2

#define PPC_MSG_TICK_BROADCAST	2

#define PPC_MSG_DEBUGGER_BREAK  3



/* for irq controllers that have dedicated ipis per message (4) */

arch/powerpc/include/asm/time.h

+1 −0
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ extern struct clock_event_device decrementer_clockevent; 
struct rtc_time;

extern void to_tm(int tim, struct rtc_time * tm);

extern void GregorianDay(struct rtc_time *tm);

extern void tick_broadcast_ipi_handler(void);



extern void generic_calibrate_decr(void);

arch/powerpc/kernel/smp.c

+17 −4
Original line number Diff line number Diff line
@@ -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>
@@ -145,9 +146,9 @@ static irqreturn_t reschedule_action(int irq, void *data) 
	return IRQ_HANDLED;

}



static irqreturn_t unused_action(int irq, void *data)

static irqreturn_t tick_broadcast_ipi_action(int irq, void *data)

{

	/* This slot is unused and hence available for use, if needed */

	tick_broadcast_ipi_handler();

	return IRQ_HANDLED;

}
@@ -168,14 +169,14 @@ static irqreturn_t debug_ipi_action(int irq, void *data) 
static irq_handler_t smp_ipi_action[] = {

	[PPC_MSG_CALL_FUNCTION] =  call_function_action,

	[PPC_MSG_RESCHEDULE] = reschedule_action,

	[PPC_MSG_UNUSED] = unused_action,

	[PPC_MSG_TICK_BROADCAST] = tick_broadcast_ipi_action,

	[PPC_MSG_DEBUGGER_BREAK] = debug_ipi_action,

};



const char *smp_ipi_name[] = {

	[PPC_MSG_CALL_FUNCTION] =  "ipi call function",

	[PPC_MSG_RESCHEDULE] = "ipi reschedule",

	[PPC_MSG_UNUSED] = "ipi unused",

	[PPC_MSG_TICK_BROADCAST] = "ipi tick-broadcast",

	[PPC_MSG_DEBUGGER_BREAK] = "ipi debugger",

};
@@ -251,6 +252,8 @@ irqreturn_t smp_ipi_demux(void) 
			generic_smp_call_function_interrupt();

		if (all & IPI_MESSAGE(PPC_MSG_RESCHEDULE))

			scheduler_ipi();

		if (all & IPI_MESSAGE(PPC_MSG_TICK_BROADCAST))

			tick_broadcast_ipi_handler();

		if (all & IPI_MESSAGE(PPC_MSG_DEBUGGER_BREAK))

			debug_ipi_action(0, NULL);

	} while (info->messages);
@@ -289,6 +292,16 @@ void arch_send_call_function_ipi_mask(const struct cpumask *mask) 
		do_message_pass(cpu, PPC_MSG_CALL_FUNCTION);

}



#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST

void tick_broadcast(const struct cpumask *mask)

{

	unsigned int cpu;



	for_each_cpu(cpu, mask)

		do_message_pass(cpu, PPC_MSG_TICK_BROADCAST);

}

#endif



#if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)

void smp_send_debugger_break(void)

{

arch/powerpc/kernel/time.c

+5 −0
Original line number Diff line number Diff line
@@ -825,6 +825,11 @@ static void decrementer_set_mode(enum clock_event_mode mode, 
		decrementer_set_next_event(DECREMENTER_MAX, dev);

}



/* Interrupt handler for the timer broadcast IPI */

void tick_broadcast_ipi_handler(void)

{

}



static void register_decrementer_clockevent(int cpu)

{

	struct clock_event_device *dec = &per_cpu(decrementers, cpu);

arch/powerpc/platforms/cell/interrupt.c

+1 −1
Original line number Diff line number Diff line
@@ -215,7 +215,7 @@ void iic_request_IPIs(void) 
{

	iic_request_ipi(PPC_MSG_CALL_FUNCTION);

	iic_request_ipi(PPC_MSG_RESCHEDULE);

	iic_request_ipi(PPC_MSG_UNUSED);

	iic_request_ipi(PPC_MSG_TICK_BROADCAST);

	iic_request_ipi(PPC_MSG_DEBUGGER_BREAK);

}

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