Commit b2d3d61a authored by Daniel Lezcano's avatar Daniel Lezcano Committed by Thomas Gleixner
Browse files

genirq/timings: Add infrastructure to track the interrupt timings 



The interrupt framework gives a lot of information about each interrupt. It
does not keep track of when those interrupts occur though, which is a
prerequisite for estimating the next interrupt arrival for power management
purposes.

Add a mechanism to record the timestamp for each interrupt occurrences in a
per-CPU circular buffer to help with the prediction of the next occurrence
using a statistical model.

Each CPU can store up to IRQ_TIMINGS_SIZE events <irq, timestamp>, the
current value of IRQ_TIMINGS_SIZE is 32.

Each event is encoded into a single u64, where the high 48 bits are used
for the timestamp and the low 16 bits are for the irq number.

A static key is introduced so when the irq prediction is switched off at
runtime, the overhead is near to zero.

It results in most of the code in internals.h for inline reasons and a very
few in the new file timings.c. The latter will contain more in the next patch
which will provide the statistical model for the next event prediction.

Signed-off-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarNicolas Pitre <nicolas.pitre@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Rafael J . Wysocki" <rafael@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Link: http://lkml.kernel.org/r/1498227072-5980-1-git-send-email-daniel.lezcano@linaro.org
parent c2ce34c0

include/linux/interrupt.h

+5 −0
Original line number Diff line number Diff line
@@ -703,6 +703,11 @@ static inline void init_irq_proc(void) 
}

#endif



#ifdef CONFIG_IRQ_TIMINGS

void irq_timings_enable(void);

void irq_timings_disable(void);

#endif



struct seq_file;

int show_interrupts(struct seq_file *p, void *v);

int arch_show_interrupts(struct seq_file *p, int prec);

kernel/irq/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -85,6 +85,9 @@ config GENERIC_MSI_IRQ_DOMAIN 
config HANDLE_DOMAIN_IRQ

	bool



config IRQ_TIMINGS

	bool



config IRQ_DOMAIN_DEBUG

	bool "Expose hardware/virtual IRQ mapping via debugfs"

	depends on IRQ_DOMAIN && DEBUG_FS

kernel/irq/Makefile

+1 −0
Original line number Diff line number Diff line 


obj-y := irqdesc.o handle.o manage.o spurious.o resend.o chip.o dummychip.o devres.o

obj-$(CONFIG_IRQ_TIMINGS) += timings.o

obj-$(CONFIG_GENERIC_IRQ_CHIP) += generic-chip.o

obj-$(CONFIG_GENERIC_IRQ_PROBE) += autoprobe.o

obj-$(CONFIG_IRQ_DOMAIN) += irqdomain.o

kernel/irq/handle.c

+2 −0
Original line number Diff line number Diff line
@@ -138,6 +138,8 @@ irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc, unsigned int *flags 
	unsigned int irq = desc->irq_data.irq;

	struct irqaction *action;



	record_irq_time(desc);



	for_each_action_of_desc(desc, action) {

		irqreturn_t res;

kernel/irq/internals.h

+90 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#include <linux/irqdesc.h>

#include <linux/kernel_stat.h>

#include <linux/pm_runtime.h>

#include <linux/sched/clock.h>



#ifdef CONFIG_SPARSE_IRQ

# define IRQ_BITMAP_BITS	(NR_IRQS + 8196)
@@ -57,6 +58,7 @@ enum { 
	IRQS_WAITING		= 0x00000080,

	IRQS_PENDING		= 0x00000200,

	IRQS_SUSPENDED		= 0x00000800,

	IRQS_TIMINGS		= 0x00001000,

};



#include "debug.h"
@@ -255,6 +257,94 @@ static inline void 
irq_pm_remove_action(struct irq_desc *desc, struct irqaction *action) { }

#endif



#ifdef CONFIG_IRQ_TIMINGS



#define IRQ_TIMINGS_SHIFT	5

#define IRQ_TIMINGS_SIZE	(1 << IRQ_TIMINGS_SHIFT)

#define IRQ_TIMINGS_MASK	(IRQ_TIMINGS_SIZE - 1)



/**

 * struct irq_timings - irq timings storing structure

 * @values: a circular buffer of u64 encoded <timestamp,irq> values

 * @count: the number of elements in the array

 */

struct irq_timings {

	u64	values[IRQ_TIMINGS_SIZE];

	int	count;

};



DECLARE_PER_CPU(struct irq_timings, irq_timings);



static inline void irq_remove_timings(struct irq_desc *desc)

{

	desc->istate &= ~IRQS_TIMINGS;

}



static inline void irq_setup_timings(struct irq_desc *desc, struct irqaction *act)

{

	/*

	 * We don't need the measurement because the idle code already

	 * knows the next expiry event.

	 */

	if (act->flags & __IRQF_TIMER)

		return;



	desc->istate |= IRQS_TIMINGS;

}



extern void irq_timings_enable(void);

extern void irq_timings_disable(void);



DECLARE_STATIC_KEY_FALSE(irq_timing_enabled);



/*

 * The interrupt number and the timestamp are encoded into a single

 * u64 variable to optimize the size.

 * 48 bit time stamp and 16 bit IRQ number is way sufficient.

 *  Who cares an IRQ after 78 hours of idle time?

 */

static inline u64 irq_timing_encode(u64 timestamp, int irq)

{

	return (timestamp << 16) | irq;

}



static inline int irq_timing_decode(u64 value, u64 *timestamp)

{

	*timestamp = value >> 16;

	return value & U16_MAX;

}



/*

 * The function record_irq_time is only called in one place in the

 * interrupts handler. We want this function always inline so the code

 * inside is embedded in the function and the static key branching

 * code can act at the higher level. Without the explicit

 * __always_inline we can end up with a function call and a small

 * overhead in the hotpath for nothing.

 */

static __always_inline void record_irq_time(struct irq_desc *desc)

{

	if (!static_branch_likely(&irq_timing_enabled))

		return;



	if (desc->istate & IRQS_TIMINGS) {

		struct irq_timings *timings = this_cpu_ptr(&irq_timings);



		timings->values[timings->count & IRQ_TIMINGS_MASK] =

			irq_timing_encode(local_clock(),

					  irq_desc_get_irq(desc));



		timings->count++;

	}

}

#else

static inline void irq_remove_timings(struct irq_desc *desc) {}

static inline void irq_setup_timings(struct irq_desc *desc,

				     struct irqaction *act) {};

static inline void record_irq_time(struct irq_desc *desc) {}

#endif /* CONFIG_IRQ_TIMINGS */





#ifdef CONFIG_GENERIC_IRQ_CHIP

void irq_init_generic_chip(struct irq_chip_generic *gc, const char *name,

			   int num_ct, unsigned int irq_base,

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