Re: [patch 14/30] drm/i915/pmu: Replace open coded kstat_irqs() copy
From: Tvrtko Ursulin
Date: Fri Dec 11 2020 - 05:17:14 EST
On 10/12/2020 19:25, Thomas Gleixner wrote:
Driver code has no business with the internals of the irq descriptor.
Aside of that the count is per interrupt line and therefore takes
interrupts from other devices into account which share the interrupt line
and are not handled by the graphics driver.
Replace it with a pmu private count which only counts interrupts which
originate from the graphics card.
To avoid atomics or heuristics of some sort make the counter field
'unsigned long'. That limits the count to 4e9 on 32bit which is a lot and
postprocessing can easily deal with the occasional wraparound.
After my failed hasty sketch from last night I had a different one which
was kind of heuristics based (re-reading the upper dword and retrying if
it changed on 32-bit). But you are right - it is okay to at least start
like this today and if later there is a need we can either do that or
deal with wrap at PMU read time.
So thanks for dealing with it, some small comments below but overall it
is fine.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
---
drivers/gpu/drm/i915/i915_irq.c | 34 ++++++++++++++++++++++++++++++++++
drivers/gpu/drm/i915/i915_pmu.c | 18 +-----------------
drivers/gpu/drm/i915/i915_pmu.h | 8 ++++++++
3 files changed, 43 insertions(+), 17 deletions(-)
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -60,6 +60,24 @@
* and related files, but that will be described in separate chapters.
*/
+/*
+ * Interrupt statistic for PMU. Increments the counter only if the
+ * interrupt originated from the the GPU so interrupts from a device which
+ * shares the interrupt line are not accounted.
+ */
+static inline void pmu_irq_stats(struct drm_i915_private *priv,
We never use priv as a local name, it should be either i915 or dev_priv.
+ irqreturn_t res)
+{
+ if (unlikely(res != IRQ_HANDLED))
+ return;
+
+ /*
+ * A clever compiler translates that into INC. A not so clever one
+ * should at least prevent store tearing.
+ */
+ WRITE_ONCE(priv->pmu.irq_count, priv->pmu.irq_count + 1);
Curious, probably more educational for me - given x86_32 and x86_64, and
the context of it getting called, what is the difference from just doing
irq_count++?
+}
+
typedef bool (*long_pulse_detect_func)(enum hpd_pin pin, u32 val);
static const u32 hpd_ilk[HPD_NUM_PINS] = {
@@ -1599,6 +1617,8 @@ static irqreturn_t valleyview_irq_handle
valleyview_pipestat_irq_handler(dev_priv, pipe_stats);
} while (0);
+ pmu_irq_stats(dev_priv, ret);
+
enable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
return ret;
@@ -1676,6 +1696,8 @@ static irqreturn_t cherryview_irq_handle
valleyview_pipestat_irq_handler(dev_priv, pipe_stats);
} while (0);
+ pmu_irq_stats(dev_priv, ret);
+
enable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
return ret;
@@ -2103,6 +2125,8 @@ static irqreturn_t ilk_irq_handler(int i
if (sde_ier)
raw_reg_write(regs, SDEIER, sde_ier);
+ pmu_irq_stats(i915, ret);
+
/* IRQs are synced during runtime_suspend, we don't require a wakeref */
enable_rpm_wakeref_asserts(&i915->runtime_pm);
@@ -2419,6 +2443,8 @@ static irqreturn_t gen8_irq_handler(int
gen8_master_intr_enable(regs);
+ pmu_irq_stats(dev_priv, IRQ_HANDLED);
+
return IRQ_HANDLED;
}
@@ -2514,6 +2540,8 @@ static __always_inline irqreturn_t
gen11_gu_misc_irq_handler(gt, gu_misc_iir);
+ pmu_irq_stats(i915, IRQ_HANDLED);
+
return IRQ_HANDLED;
}
@@ -3688,6 +3716,8 @@ static irqreturn_t i8xx_irq_handler(int
i8xx_pipestat_irq_handler(dev_priv, iir, pipe_stats);
} while (0);
+ pmu_irq_stats(dev_priv, ret);
+
enable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
return ret;
@@ -3796,6 +3826,8 @@ static irqreturn_t i915_irq_handler(int
i915_pipestat_irq_handler(dev_priv, iir, pipe_stats);
} while (0);
+ pmu_irq_stats(dev_priv, ret);
+
enable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
return ret;
@@ -3941,6 +3973,8 @@ static irqreturn_t i965_irq_handler(int
i965_pipestat_irq_handler(dev_priv, iir, pipe_stats);
} while (0);
+ pmu_irq_stats(dev_priv, IRQ_HANDLED);
+
enable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
return ret;
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -423,22 +423,6 @@ static enum hrtimer_restart i915_sample(
return HRTIMER_RESTART;
}
In this file you can also drop the #include <linux/irq.h> line.
-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 =
@@ -581,7 +565,7 @@ static u64 __i915_pmu_event_read(struct
USEC_PER_SEC /* to MHz */);
break;
case I915_PMU_INTERRUPTS:
- val = count_interrupts(i915);
+ val = READ_ONCE(pmu->irq_count);
I guess same curiosity about READ_ONCE like in the increment site.
break;
case I915_PMU_RC6_RESIDENCY:
val = get_rc6(&i915->gt);
--- a/drivers/gpu/drm/i915/i915_pmu.h
+++ b/drivers/gpu/drm/i915/i915_pmu.h
@@ -108,6 +108,14 @@ struct i915_pmu {
*/
ktime_t sleep_last;
/**
+ * @irq_count: Number of interrupts
+ *
+ * Intentionally unsigned long to avoid atomics or heuristics on 32bit.
+ * 4e9 interrupts are a lot and postprocessing can really deal with an
+ * occasional wraparound easily. It's 32bit after all.
+ */
+ unsigned long irq_count;
+ /**
* @events_attr_group: Device events attribute group.
*/
struct attribute_group events_attr_group;
Regards,
Tvrtko