Message-Id: <1455637383-14412-1-git-send-email-daniel.lezcano@linaro.org>
Date:	Tue, 16 Feb 2016 16:43:02 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	tglx@...utronix.de
Cc:	peterz@...radead.org, rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, nicolas.pitre@...aro.org,
	vincent.guittot@...aro.org
Subject: [PATCH V3 1/2] irq: 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.

This patch provides a mean to record the elapsed time between successive
interrupt occurrences in a per-IRQ per-CPU circular buffer to help with
the prediction of the next occurrence using a statistical model.

A new function is added to browse the different interrupts and retrieve the
timing information stored in it.

A static key will be introduced when the irq prediction is switched on at
runtime in order to reduce an overhead near to zero when the kernel is not
using it.

Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
---
 include/linux/interrupt.h |  17 +++++++
 include/linux/irqdesc.h   |   4 ++
 kernel/irq/Kconfig        |   3 ++
 kernel/irq/Makefile       |   1 +
 kernel/irq/handle.c       |   2 +
 kernel/irq/internals.h    |  42 ++++++++++++++++++
 kernel/irq/irqdesc.c      |  10 +++++
 kernel/irq/manage.c       |   3 ++
 kernel/irq/timings.c      | 110 ++++++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 192 insertions(+)
 create mode 100644 kernel/irq/timings.c

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 0e95fcc..f053596 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -665,6 +665,23 @@ static inline void init_irq_proc(void)
 }
 #endif
 
+#ifdef CONFIG_IRQ_TIMINGS
+
+#define IRQ_TIMINGS_SHIFT	2
+#define IRQ_TIMINGS_SIZE	(1 << IRQ_TIMINGS_SHIFT)
+#define IRQ_TIMINGS_MASK	(IRQ_TIMINGS_SIZE - 1)
+
+struct irq_timings {
+	u32 values[IRQ_TIMINGS_SIZE];	/* our circular buffer */
+	u64 sum;			/* sum of values */
+	u64 timestamp;			/* latest timestamp */
+	unsigned int w_index;		/* current buffer index */
+};
+
+struct irq_timings *irqtiming_get_next(int *irq);
+
+#endif
+
 struct seq_file;
 int show_interrupts(struct seq_file *p, void *v);
 int arch_show_interrupts(struct seq_file *p, int prec);
diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index dcca77c..f4e29b2 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -12,6 +12,7 @@ struct proc_dir_entry;
 struct module;
 struct irq_desc;
 struct irq_domain;
+struct irq_timings;
 struct pt_regs;
 
 /**
@@ -51,6 +52,9 @@ struct irq_desc {
 	struct irq_data		irq_data;
 	unsigned int __percpu	*kstat_irqs;
 	irq_flow_handler_t	handle_irq;
+#ifdef CONFIG_IRQ_TIMINGS
+	struct irq_timings __percpu *timings;
+#endif
 #ifdef CONFIG_IRQ_PREFLOW_FASTEOI
 	irq_preflow_handler_t	preflow_handler;
 #endif
diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index 3b48dab..392c9f5 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -77,6 +77,9 @@ 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
diff --git a/kernel/irq/Makefile b/kernel/irq/Makefile
index 2fc9cbd..9c6d3e8 100644
--- a/kernel/irq/Makefile
+++ b/kernel/irq/Makefile
@@ -8,3 +8,4 @@ obj-$(CONFIG_GENERIC_PENDING_IRQ) += migration.o
 obj-$(CONFIG_GENERIC_IRQ_MIGRATION) += cpuhotplug.o
 obj-$(CONFIG_PM_SLEEP) += pm.o
 obj-$(CONFIG_GENERIC_MSI_IRQ) += msi.o
+obj-$(CONFIG_IRQ_TIMINGS) += timings.o
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index a15b548..cd37536 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -138,6 +138,8 @@ irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
 	unsigned int flags = 0, irq = desc->irq_data.irq;
 	struct irqaction *action;
 
+	handle_timings(desc);
+
 	for_each_action_of_desc(desc, action) {
 		irqreturn_t res;
 
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index eab521fc..3d100af 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -56,6 +56,7 @@ enum {
 	IRQS_WAITING		= 0x00000080,
 	IRQS_PENDING		= 0x00000200,
 	IRQS_SUSPENDED		= 0x00000800,
+	IRQS_TIMINGS		= 0x00001000,
 };
 
 #include "debug.h"
@@ -218,3 +219,44 @@ irq_pm_install_action(struct irq_desc *desc, struct irqaction *action) { }
 static inline void
 irq_pm_remove_action(struct irq_desc *desc, struct irqaction *action) { }
 #endif
+
+#ifdef CONFIG_IRQ_TIMINGS
+static inline int alloc_timings(struct irq_desc *desc)
+{
+	desc->timings = alloc_percpu(struct irq_timings);
+	if (!desc->timings)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static inline void free_timings(struct irq_desc *desc)
+{
+	free_percpu(desc->timings);
+}
+
+static inline void remove_timings(struct irq_desc *desc)
+{
+	desc->istate &= ~IRQS_TIMINGS;
+}
+
+static inline void setup_timings(struct irq_desc *desc, struct irqaction *act)
+{
+	/*
+	 * Timers are deterministic, so no need to do any measurement
+	 * on them.
+	 */
+	if (act->flags & __IRQF_TIMER)
+		return;
+
+	desc->istate |= IRQS_TIMINGS;
+}
+extern void handle_timings(struct irq_desc *desc);
+#else
+static inline int alloc_timings(struct irq_desc *desc) { return 0; }
+static inline void free_timings(struct irq_desc *desc) {}
+static inline void handle_timings(struct irq_desc *desc) {}
+static inline void remove_timings(struct irq_desc *desc) {}
+static inline void setup_timings(struct irq_desc *desc,
+				 struct irqaction *act) {};
+#endif
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 0ccd028..577686b 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -174,6 +174,9 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
 	if (alloc_masks(desc, gfp, node))
 		goto err_kstat;
 
+	if (alloc_timings(desc))
+		goto err_mask;
+
 	raw_spin_lock_init(&desc->lock);
 	lockdep_set_class(&desc->lock, &irq_desc_lock_class);
 	init_rcu_head(&desc->rcu);
@@ -182,6 +185,8 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner)
 
 	return desc;
 
+err_mask:
+	free_masks(desc);
 err_kstat:
 	free_percpu(desc->kstat_irqs);
 err_desc:
@@ -220,6 +225,11 @@ static void free_desc(unsigned int irq)
 	 * the child interrupts.
 	 */
 	call_rcu(&desc->rcu, delayed_free_desc);
+
+	free_timings(desc);
+	free_masks(desc);
+	free_percpu(desc->kstat_irqs);
+	kfree(desc);
 }
 
 static int alloc_descs(unsigned int start, unsigned int cnt, int node,
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3ddd229..132c2d7 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1343,6 +1343,8 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
 		__enable_irq(desc);
 	}
 
+	setup_timings(desc, new);
+
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 
 	/*
@@ -1465,6 +1467,7 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
 		irq_settings_clr_disable_unlazy(desc);
 		irq_shutdown(desc);
 		irq_release_resources(desc);
+		remove_timings(desc);
 	}
 
 #ifdef CONFIG_SMP
diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c
new file mode 100644
index 0000000..95976fa0
--- /dev/null
+++ b/kernel/irq/timings.c
@@ -0,0 +1,110 @@
+/*
+ * linux/kernel/irq/timings.c
+ *
+ * Copyright (C) 2016, Linaro Ltd - Daniel Lezcano <daniel.lezcano@...aro.org>
+ *
+ */
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/irqdesc.h>
+#include <linux/percpu.h>
+
+#include "internals.h"
+
+/**
+ * handle_timings - stores an irq timing  when an interrupt occurs
+ *
+ * @desc: the irq descriptor
+ *
+ * For all interruptions with their IRQS_TIMINGS flag set, the function
+ * computes the time interval between two interrupt events and store it
+ * in a circular buffer.
+ */
+void handle_timings(struct irq_desc *desc)
+{
+	struct irq_timings *timings;
+	u64 prev, now, diff;
+
+	if (!(desc->istate & IRQS_TIMINGS))
+		return;
+
+	timings = this_cpu_ptr(desc->timings);
+	now = local_clock();
+	prev = timings->timestamp;
+	timings->timestamp = now;
+
+	/*
+	 * If it is the first interrupt of the series, we can't
+	 * compute an interval, just store the timestamp and exit.
+	 */
+	if (unlikely(!prev))
+		return;
+
+	diff = now - prev;
+
+	/*
+	 * microsec (actually 1024th of a milisec) precision is good
+	 * enough for our purpose.
+	 */
+	diff >>= 10;
+
+	/*
+	 * There is no point to store intervals from interrupts more
+	 * than ~1 second apart. Furthermore that increases the risk
+	 * of overflowing our variance computation. Reset all values
+	 * in that case. Otherwise we know the magnitude of diff is
+	 * well within 32 bits.
+	 */
+	if (unlikely(diff > USEC_PER_SEC)) {
+		memset(timings, 0, sizeof(*timings));
+		timings->timestamp = now;
+		return;
+	}
+
+	/* The oldest value corresponds to the next index. */
+	timings->w_index = (timings->w_index + 1) & IRQ_TIMINGS_MASK;
+
+	/*
+	 * Remove the oldest value from the summing. If this is the
+	 * first time we go through this array slot, the previous
+	 * value will be zero and we won't substract anything from the
+	 * current sum. Hence this code relies on a zero-ed structure.
+	 */
+	timings->sum -= timings->values[timings->w_index];
+	timings->values[timings->w_index] = diff;
+	timings->sum += diff;
+}
+
+/**
+ * irqtiming_get_next - return the next irq timing
+ *
+ * @int: an integer representing the interrupt number
+ *
+ * Returns a struct irq_timings, NULL if we reach the end of the
+ * interrupts list.
+ */
+struct irq_timings *irqtiming_get_next(int *irq)
+{
+	struct irq_desc *desc;
+	int next;
+
+again:
+	/* Do a racy lookup of the next allocated irq */
+	next = irq_get_next_irq(*irq);
+	if (next >= nr_irqs)
+		return NULL;
+
+	*irq = next + 1;
+
+	/*
+	 * Now lookup the descriptor. It's RCU protected. This
+	 * descriptor might belong to an uninteresting interrupt or
+	 * one that is not measured. Look for the next interrupt in
+	 * that case.
+	 */
+	desc = irq_to_desc(next);
+	if (!desc || !(desc->istate & IRQS_TIMINGS))
+		goto again;
+
+	return this_cpu_ptr(desc->timings);
+}
-- 
1.9.1

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