[PATCH v2 4/8] ARCv2: perf: Support sampling events using overflow interrupts

[Alexey Brodkin]

In times of ARC 700 performance counters didn't have support of
interrupt an so for ARC we only had support of non-sampling events.

Put simply only "perf stat" was functional.

Now with ARC HS we have support of interrupts in performance counters
which this change introduces support of.

ARC performance counters act in the following way in regard of
interrupts generation.
 [1] A counter counts starting from value set in PCT_COUNT register pair
 [2] Once counter reaches value set in PCT_INT_CNT interrupt is raised

Basic setup look like this:
 [1] PCT_COUNT = 0;
 [2] PCT_INT_CNT = __limit_value__;
 [3] Enable interrupts for that counter and let it run
 [4] Let counter reach its limit
 [5] Handle interrupt when it happens

Note that PCT HW block is build in CPU core and so ints interrupt
line (which is basically OR of all counters IRQs) is wired directly to
top-level IRQC. That means do de-assert PCT interrupt it's required to
reset IRQs from all counters that have reached their limit values.

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Signed-off-by: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
---

Compared to v1:
 [1] Added commit message
 [2] Removed check for is_sampling_event() because we already set
     PERF_PMU_CAP_NO_INTERRUPT in probe()
 [3] Minor cosmetics

 arch/arc/include/asm/perf_event.h |   8 ++-
 arch/arc/kernel/perf_event.c      | 127 +++++++++++++++++++++++++++++++++++---
 2 files changed, 125 insertions(+), 10 deletions(-)

diff --git a/arch/arc/include/asm/perf_event.h b/arch/arc/include/asm/perf_event.h
index ca8c414..33a6eb2 100644
--- a/arch/arc/include/asm/perf_event.h
+++ b/arch/arc/include/asm/perf_event.h
@@ -32,15 +32,19 @@
 #define ARC_REG_PCT_CONFIG	0x254
 #define ARC_REG_PCT_CONTROL	0x255
 #define ARC_REG_PCT_INDEX	0x256
+#define ARC_REG_PCT_INT_CNTL	0x25C
+#define ARC_REG_PCT_INT_CNTH	0x25D
+#define ARC_REG_PCT_INT_CTRL	0x25E
+#define ARC_REG_PCT_INT_ACT	0x25F
 
 #define ARC_REG_PCT_CONTROL_CC	(1 << 16)	/* clear counts */
 #define ARC_REG_PCT_CONTROL_SN	(1 << 17)	/* snapshot */
 
 struct arc_reg_pct_build {
 #ifdef CONFIG_CPU_BIG_ENDIAN
-	unsigned int m:8, c:8, r:6, s:2, v:8;
+	unsigned int m:8, c:8, r:5, i:1, s:2, v:8;
 #else
-	unsigned int v:8, s:2, r:6, c:8, m:8;
+	unsigned int v:8, s:2, i:1, r:5, c:8, m:8;
 #endif
 };
 
diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 2d95440..1a9f922 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -11,6 +11,7 @@
  *
  */
 #include <linux/errno.h>
+#include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/perf_event.h>
@@ -25,6 +26,7 @@ struct arc_pmu {
 	unsigned long	used_mask[BITS_TO_LONGS(ARC_PERF_MAX_COUNTERS)];
 	u64		max_period;
 	int		ev_hw_idx[PERF_COUNT_ARC_HW_MAX];
+	struct perf_event *act_counter[ARC_PERF_MAX_COUNTERS];
 	u64             raw_events[ARC_PERF_MAX_EVENTS];
 };
 
@@ -153,9 +155,11 @@ static int arc_pmu_event_init(struct perf_event *event)
 	struct hw_perf_event *hwc = &event->hw;
 	int ret;
 
-	hwc->sample_period  = arc_pmu->max_period;
-	hwc->last_period = hwc->sample_period;
-	local64_set(&hwc->period_left, hwc->sample_period);
+	if (!is_sampling_event(event)) {
+		hwc->sample_period  = arc_pmu->max_period;
+		hwc->last_period = hwc->sample_period;
+		local64_set(&hwc->period_left, hwc->sample_period);
+	}
 
 	switch (event->attr.type) {
 	case PERF_TYPE_HARDWARE:
@@ -277,6 +281,17 @@ static void arc_pmu_stop(struct perf_event *event, int flags)
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
 
+	/* Disable interrupt for this counter */
+	if (is_sampling_event(event)) {
+		/*
+		 * Reset interrupt flag by writing of 1. This is required
+		 * to make sure pending interrupt was not left.
+		 */
+		write_aux_reg(ARC_REG_PCT_INT_ACT, 1 << idx);
+		write_aux_reg(ARC_REG_PCT_INT_CTRL,
+			      read_aux_reg(ARC_REG_PCT_INT_CTRL) & ~(1 << idx));
+	}
+
 	if (!(event->hw.state & PERF_HES_STOPPED)) {
 		/* stop ARC pmu here */
 		write_aux_reg(ARC_REG_PCT_INDEX, idx);
@@ -299,6 +314,8 @@ static void arc_pmu_del(struct perf_event *event, int flags)
 	arc_pmu_stop(event, PERF_EF_UPDATE);
 	__clear_bit(event->hw.idx, arc_pmu->used_mask);
 
+	arc_pmu->act_counter[event->hw.idx] = 0;
+
 	perf_event_update_userpage(event);
 }
 
@@ -319,6 +336,20 @@ static int arc_pmu_add(struct perf_event *event, int flags)
 	}
 
 	write_aux_reg(ARC_REG_PCT_INDEX, idx);
+
+	arc_pmu->act_counter[idx] = event;
+
+	if (is_sampling_event(event)) {
+		/* Mimic full counter overflow as other arches do */
+		write_aux_reg(ARC_REG_PCT_INT_CNTL, (u32)arc_pmu->max_period);
+		write_aux_reg(ARC_REG_PCT_INT_CNTH,
+			      (arc_pmu->max_period >> 32));
+
+		/* Enable interrupt for this counter */
+		write_aux_reg(ARC_REG_PCT_INT_CTRL,
+			      read_aux_reg(ARC_REG_PCT_INT_CTRL) | (1 << idx));
+	}
+
 	write_aux_reg(ARC_REG_PCT_CONFIG, 0);
 	write_aux_reg(ARC_REG_PCT_COUNTL, 0);
 	write_aux_reg(ARC_REG_PCT_COUNTH, 0);
@@ -333,11 +364,70 @@ static int arc_pmu_add(struct perf_event *event, int flags)
 	return 0;
 }
 
+#ifdef CONFIG_ISA_ARCV2
+static irqreturn_t arc_pmu_intr(int irq, void *dev)
+{
+	struct perf_sample_data data;
+	struct arc_pmu *arc_pmu = (struct arc_pmu *)dev;
+	struct pt_regs *regs;
+	int active_ints;
+	int idx;
+
+	arc_pmu_disable(&arc_pmu->pmu);
+
+	active_ints = read_aux_reg(ARC_REG_PCT_INT_ACT);
+
+	regs = get_irq_regs();
+
+	for (idx = 0; idx < arc_pmu->n_counters; idx++) {
+		struct perf_event *event = arc_pmu->act_counter[idx];
+		struct hw_perf_event *hwc;
+
+		if (!(active_ints & (1 << idx)))
+			continue;
+
+		/* Reset interrupt flag by writing of 1 */
+		write_aux_reg(ARC_REG_PCT_INT_ACT, 1 << idx);
+
+		/*
+		 * On reset of "interrupt active" bit corresponding
+		 * "interrupt enable" bit gets automatically reset as well.
+		 * Now we need to re-enable interrupt for the counter.
+		 */
+		write_aux_reg(ARC_REG_PCT_INT_CTRL,
+			read_aux_reg(ARC_REG_PCT_INT_CTRL) | (1 << idx));
+
+		hwc = &event->hw;
+
+		WARN_ON_ONCE(hwc->idx != idx);
+
+		arc_perf_event_update(event, &event->hw, event->hw.idx);
+		perf_sample_data_init(&data, 0, hwc->last_period);
+		if (!arc_pmu_event_set_period(event))
+			continue;
+
+		if (perf_event_overflow(event, &data, regs))
+			arc_pmu_stop(event, 0);
+	}
+
+	arc_pmu_enable(&arc_pmu->pmu);
+
+	return IRQ_HANDLED;
+}
+#else
+
+static irqreturn_t arc_pmu_intr(int irq, void *dev)
+{
+	return IRQ_NONE;
+}
+
+#endif /* CONFIG_ISA_ARCV2 */
+
 static int arc_pmu_device_probe(struct platform_device *pdev)
 {
 	struct arc_reg_pct_build pct_bcr;
 	struct arc_reg_cc_build cc_bcr;
-	int i, j;
+	int i, j, has_interrupts;
 	int counter_size;	/* in bits */
 
 	struct cc_name {
@@ -364,12 +454,16 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 	if (!arc_pmu)
 		return -ENOMEM;
 
+	has_interrupts = is_isa_arcv2() ? pct_bcr.i : 0;
+
 	arc_pmu->n_counters = pct_bcr.c;
 	counter_size = 32 + (pct_bcr.s << 4);
+
 	arc_pmu->max_period = (1ULL << counter_size) - 1ULL;
 
-	pr_info("ARC perf\t: %d counters (%d bits), %d countable conditions\n",
-		arc_pmu->n_counters, counter_size, cc_bcr.c);
+	pr_info("ARC perf\t: %d counters (%d bits), %d conditions%s\n",
+		arc_pmu->n_counters, counter_size, cc_bcr.c,
+		has_interrupts ? ", [overflow IRQ support]":"");
 
 	arc_pmu->n_events = cc_bcr.c;
 
@@ -435,8 +529,25 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
 		.read		= arc_pmu_read,
 	};
 
-	/* ARC 700 PMU does not support sampling events */
-	arc_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
+	if (has_interrupts) {
+		int irq = platform_get_irq(pdev, 0);
+
+		if (irq < 0) {
+			pr_err("Cannot get IRQ number for the platform\n");
+			return -ENODEV;
+		}
+
+		ret = devm_request_irq(&pdev->dev, irq, arc_pmu_intr, 0,
+				       "arc-pmu", arc_pmu);
+		if (ret) {
+			pr_err("could not allocate PMU IRQ\n");
+			return ret;
+		}
+
+		/* Clean all pending interrupt flags */
+		write_aux_reg(ARC_REG_PCT_INT_ACT, 0xffffffff);
+	} else
+		arc_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 
 	return perf_pmu_register(&arc_pmu->pmu, pdev->name, PERF_TYPE_RAW);
 }
-- 
2.4.3

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