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Commit 4ace6139 authored by Alex Smith's avatar Alex Smith Committed by Ralf Baechle
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MIPS: SMP: Don't increment irq_count multiple times for call function IPIs 



The majority of SMP platforms handle their IPIs through do_IRQ()
which calls irq_{enter/exit}(). When a call function IPI is received,
smp_call_function_interrupt() is called which also calls
irq_{enter,exit}(), meaning irq_count is raised twice.

When tick broadcasting is used (which is implemented via a call
function IPI), this incorrectly causes all CPU idle time on the core
receiving broadcast ticks to be accounted as time spent servicing
IRQs, as account_process_tick() will account as such if irq_count is
greater than 1. This results in 100% CPU usage being reported on a
core which receives its ticks via broadcast.

This patch removes the SMP smp_call_function_interrupt() wrapper which
calls irq_{enter,exit}(). Platforms which handle their IPIs through
do_IRQ() now call generic_smp_call_function_interrupt() directly to
avoid incrementing irq_count a second time. Platforms which don't
(loongson, sgi-ip27, sibyte) call generic_smp_call_function_interrupt()
wrapped in irq_{enter,exit}().

Signed-off-by: default avatarAlex Smith <alex.smith@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10770/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 55fdcb2d

arch/mips/cavium-octeon/smp.c

+1 −1
Original line number Original line Diff line number Diff line
@@ -42,7 +42,7 @@ static irqreturn_t mailbox_interrupt(int irq, void *dev_id) 
	cvmx_write_csr(CVMX_CIU_MBOX_CLRX(coreid), action);

	cvmx_write_csr(CVMX_CIU_MBOX_CLRX(coreid), action);





	if (action & SMP_CALL_FUNCTION)

	if (action & SMP_CALL_FUNCTION)

		smp_call_function_interrupt();

		generic_smp_call_function_interrupt();

	if (action & SMP_RESCHEDULE_YOURSELF)

	if (action & SMP_RESCHEDULE_YOURSELF)

		scheduler_ipi();

		scheduler_ipi();

arch/mips/include/asm/smp.h

+0 −2
Original line number Original line Diff line number Diff line
@@ -83,8 +83,6 @@ static inline void __cpu_die(unsigned int cpu) 
extern void play_dead(void);

extern void play_dead(void);

#endif

#endif





extern asmlinkage void smp_call_function_interrupt(void);



static inline void arch_send_call_function_single_ipi(int cpu)

static inline void arch_send_call_function_single_ipi(int cpu)

{

{

	extern struct plat_smp_ops *mp_ops;	/* private */

	extern struct plat_smp_ops *mp_ops;	/* private */

arch/mips/kernel/smp-bmips.c

+2 −2
Original line number Original line Diff line number Diff line
@@ -284,7 +284,7 @@ static irqreturn_t bmips5000_ipi_interrupt(int irq, void *dev_id) 
	if (action == 0)

	if (action == 0)

		scheduler_ipi();

		scheduler_ipi();

	else

	else

		smp_call_function_interrupt();

		generic_smp_call_function_interrupt();





	return IRQ_HANDLED;

	return IRQ_HANDLED;

}

}
@@ -336,7 +336,7 @@ static irqreturn_t bmips43xx_ipi_interrupt(int irq, void *dev_id) 
	if (action & SMP_RESCHEDULE_YOURSELF)

	if (action & SMP_RESCHEDULE_YOURSELF)

		scheduler_ipi();

		scheduler_ipi();

	if (action & SMP_CALL_FUNCTION)

	if (action & SMP_CALL_FUNCTION)

		smp_call_function_interrupt();

		generic_smp_call_function_interrupt();





	return IRQ_HANDLED;

	return IRQ_HANDLED;

}

}

arch/mips/kernel/smp.c

+0 −10
Original line number Original line Diff line number Diff line
@@ -192,16 +192,6 @@ asmlinkage void start_secondary(void) 
	cpu_startup_entry(CPUHP_ONLINE);

	cpu_startup_entry(CPUHP_ONLINE);

}

}





/*

 * Call into both interrupt handlers, as we share the IPI for them

 */

void __irq_entry smp_call_function_interrupt(void)

{

	irq_enter();

	generic_smp_call_function_interrupt();

	irq_exit();

}



static void stop_this_cpu(void *dummy)

static void stop_this_cpu(void *dummy)

{

{

	/*

	/*

arch/mips/lantiq/irq.c

+1 −1
Original line number Original line Diff line number Diff line
@@ -293,7 +293,7 @@ static irqreturn_t ipi_resched_interrupt(int irq, void *dev_id) 




static irqreturn_t ipi_call_interrupt(int irq, void *dev_id)

static irqreturn_t ipi_call_interrupt(int irq, void *dev_id)

{

{

	smp_call_function_interrupt();

	generic_smp_call_function_interrupt();

	return IRQ_HANDLED;

	return IRQ_HANDLED;

}

}