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authorDaniel Lezcano <daniel.lezcano@linaro.org>2017-06-23 16:11:07 +0200
committerThomas Gleixner <tglx@linutronix.de>2017-06-24 11:44:11 +0200
commitb2d3d61adb7b73cfe5f82404f7a130a76fc64232 (patch)
treea82a3e94b60f69dfd7607bee494c3f980b518177 /kernel/irq/internals.h
parentc2ce34c0a0e5187195ecade872be950d2611ba68 (diff)
downloadlinux-stericsson-b2d3d61adb7b73cfe5f82404f7a130a76fc64232.tar.gz
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: Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Nicolas 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
Diffstat (limited to 'kernel/irq/internals.h')
-rw-r--r--kernel/irq/internals.h90
1 files changed, 90 insertions, 0 deletions
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index a573e0771baf..b95b74920433 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -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,