[Intel-gfx] [PATCH] drm/i915/pmu: Stop peeking at kernel internals for counting interrupts

* [Intel-gfx] [PATCH] drm/i915/pmu: Stop peeking at kernel internals for counting interrupts
@ 2020-12-10 17:35 Tvrtko Ursulin
  2020-12-10 18:29 ` Chris Wilson
                   ` (3 more replies)
  0 siblings, 4 replies; 5+ messages in thread
From: Tvrtko Ursulin @ 2020-12-10 17:35 UTC (permalink / raw)
  To: Intel-gfx; +Cc: Thomas Gleixner, Chris Wilson

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Peeking at kernel internals is bad taste so instead we keep our own
counter which also solves the problem of shared interrupt lines.

Additional cost should be way below noise relative to mmio reads.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h |  3 +++
 drivers/gpu/drm/i915/i915_irq.c | 16 ++++++++++++++++
 drivers/gpu/drm/i915/i915_pmu.c | 19 +------------------
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5d04b282c060..de5cdcdc46b0 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -889,6 +889,9 @@ struct drm_i915_private {
 	/* protects the irq masks */
 	spinlock_t irq_lock;
 
+	/** Overall irq handler invocations. */
+	u64 irq_count;
+
 	bool display_irqs_enabled;
 
 	/* To control wakeup latency, e.g. for irq-driven dp aux transfers. */
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b245109f73e3..a88c1da025f1 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1596,6 +1596,8 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	dev_priv->irq_count++;
+
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
 
@@ -1681,6 +1683,8 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	dev_priv->irq_count++;
+
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
 
@@ -2103,6 +2107,8 @@ static irqreturn_t ilk_irq_handler(int irq, void *arg)
 	if (unlikely(!intel_irqs_enabled(i915)))
 		return IRQ_NONE;
 
+	i915->irq_count++;
+
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(&i915->runtime_pm);
 
@@ -2523,6 +2529,8 @@ static irqreturn_t gen8_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	dev_priv->irq_count++;
+
 	master_ctl = gen8_master_intr_disable(regs);
 	if (!master_ctl) {
 		gen8_master_intr_enable(regs);
@@ -2617,6 +2625,8 @@ __gen11_irq_handler(struct drm_i915_private * const i915,
 	if (!intel_irqs_enabled(i915))
 		return IRQ_NONE;
 
+	i915->irq_count++;
+
 	master_ctl = intr_disable(regs);
 	if (!master_ctl) {
 		intr_enable(regs);
@@ -3902,6 +3912,8 @@ static irqreturn_t i8xx_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	dev_priv->irq_count++;
+
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
 
@@ -4003,6 +4015,8 @@ static irqreturn_t i915_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	dev_priv->irq_count++;
+
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
 
@@ -4147,6 +4161,8 @@ static irqreturn_t i965_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	dev_priv->irq_count++;
+
 	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
 	disable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
 
diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 97bb4aaa5236..0f313f4546ab 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -4,7 +4,6 @@
  * Copyright © 2017-2018 Intel Corporation
  */
 
-#include <linux/irq.h>
 #include <linux/pm_runtime.h>
 
 #include "gt/intel_engine.h"
@@ -452,22 +451,6 @@ static enum hrtimer_restart i915_sample(struct hrtimer *hrtimer)
 	return HRTIMER_RESTART;
 }
 
-static u64 count_interrupts(struct drm_i915_private *i915)
-{
-	/* open-coded kstat_irqs() */
-	struct irq_desc *desc = irq_to_desc(i915->drm.pdev->irq);
-	u64 sum = 0;
-	int cpu;
-
-	if (!desc || !desc->kstat_irqs)
-		return 0;
-
-	for_each_possible_cpu(cpu)
-		sum += *per_cpu_ptr(desc->kstat_irqs, cpu);
-
-	return sum;
-}
-
 static void i915_pmu_event_destroy(struct perf_event *event)
 {
 	struct drm_i915_private *i915 =
@@ -618,7 +601,7 @@ static u64 __i915_pmu_event_read(struct perf_event *event)
 				   USEC_PER_SEC /* to MHz */);
 			break;
 		case I915_PMU_INTERRUPTS:
-			val = count_interrupts(i915);
+			val = i915->irq_count;
 			break;
 		case I915_PMU_RC6_RESIDENCY:
 			val = get_rc6(&i915->gt);
-- 
2.25.1

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