arm64: perf: Add support for chaining event counters

Add support for 64bit event by using chained event counters
and 64bit cycle counters.

PMUv3 allows chaining a pair of adjacent 32-bit counters, effectively
forming a 64-bit counter. The low/even counter is programmed to count
the event of interest, and the high/odd counter is programmed to count
the CHAIN event, taken when the low/even counter overflows.

For CPU cycles, when 64bit mode is requested, the cycle counter
is used in 64bit mode. If the cycle counter is not available,
falls back to chaining.

Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/perf_event.c

@@ -446,9 +446,16 @@ static struct attribute_group armv8_pmuv3_events_attr_group = {
 };
 
 PMU_FORMAT_ATTR(event, "config:0-15");
+PMU_FORMAT_ATTR(long, "config1:0");
+
+static inline bool armv8pmu_event_is_64bit(struct perf_event *event)
+{
+	return event->attr.config1 & 0x1;
+}
 
 static struct attribute *armv8_pmuv3_format_attrs[] = {
 	&format_attr_event.attr,
+	&format_attr_long.attr,
 	NULL,
 };
 
@@ -465,6 +472,21 @@ static struct attribute_group armv8_pmuv3_format_attr_group = {
 #define	ARMV8_IDX_COUNTER_LAST(cpu_pmu) \
 	(ARMV8_IDX_CYCLE_COUNTER + cpu_pmu->num_events - 1)
 
+/*
+ * We must chain two programmable counters for 64 bit events,
+ * except when we have allocated the 64bit cycle counter (for CPU
+ * cycles event). This must be called only when the event has
+ * a counter allocated.
+ */
+static inline bool armv8pmu_event_is_chained(struct perf_event *event)
+{
+	int idx = event->hw.idx;
+
+	return !WARN_ON(idx < 0) &&
+	       armv8pmu_event_is_64bit(event) &&
+	       (idx != ARMV8_IDX_CYCLE_COUNTER);
+}
+
 /*
  * ARMv8 low level PMU access
  */
@@ -516,12 +538,23 @@ static inline u32 armv8pmu_read_evcntr(int idx)
 	return read_sysreg(pmxevcntr_el0);
 }
 
+static inline u64 armv8pmu_read_hw_counter(struct perf_event *event)
+{
+	int idx = event->hw.idx;
+	u64 val = 0;
+
+	val = armv8pmu_read_evcntr(idx);
+	if (armv8pmu_event_is_chained(event))
+		val = (val << 32) | armv8pmu_read_evcntr(idx - 1);
+	return val;
+}
+
 static inline u64 armv8pmu_read_counter(struct perf_event *event)
 {
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
 	struct hw_perf_event *hwc = &event->hw;
 	int idx = hwc->idx;
-	u32 value = 0;
+	u64 value = 0;
 
 	if (!armv8pmu_counter_valid(cpu_pmu, idx))
 		pr_err("CPU%u reading wrong counter %d\n",
@@ -529,7 +562,7 @@ static inline u64 armv8pmu_read_counter(struct perf_event *event)
 	else if (idx == ARMV8_IDX_CYCLE_COUNTER)
 		value = read_sysreg(pmccntr_el0);
 	else
-		value = armv8pmu_read_evcntr(idx);
+		value = armv8pmu_read_hw_counter(event);
 
 	return value;
 }
@@ -540,6 +573,19 @@ static inline void armv8pmu_write_evcntr(int idx, u32 value)
 	write_sysreg(value, pmxevcntr_el0);
 }
 
+static inline void armv8pmu_write_hw_counter(struct perf_event *event,
+					     u64 value)
+{
+	int idx = event->hw.idx;
+
+	if (armv8pmu_event_is_chained(event)) {
+		armv8pmu_write_evcntr(idx, upper_32_bits(value));
+		armv8pmu_write_evcntr(idx - 1, lower_32_bits(value));
+	} else {
+		armv8pmu_write_evcntr(idx, value);
+	}
+}
+
 static inline void armv8pmu_write_counter(struct perf_event *event, u64 value)
 {
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
@@ -551,14 +597,16 @@ static inline void armv8pmu_write_counter(struct perf_event *event, u64 value)
 			smp_processor_id(), idx);
 	else if (idx == ARMV8_IDX_CYCLE_COUNTER) {
 		/*
-		 * Set the upper 32bits as this is a 64bit counter but we only
-		 * count using the lower 32bits and we want an interrupt when
-		 * it overflows.
+		 * The cycles counter is really a 64-bit counter.
+		 * When treating it as a 32-bit counter, we only count
+		 * the lower 32 bits, and set the upper 32-bits so that
+		 * we get an interrupt upon 32-bit overflow.
 		 */
-		value |= 0xffffffff00000000ULL;
+		if (!armv8pmu_event_is_64bit(event))
+			value |= 0xffffffff00000000ULL;
 		write_sysreg(value, pmccntr_el0);
 	} else
-		armv8pmu_write_evcntr(idx, value);
+		armv8pmu_write_hw_counter(event, value);
 }
 
 static inline void armv8pmu_write_evtype(int idx, u32 val)
@@ -568,6 +616,27 @@ static inline void armv8pmu_write_evtype(int idx, u32 val)
 	write_sysreg(val, pmxevtyper_el0);
 }
 
+static inline void armv8pmu_write_event_type(struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+	int idx = hwc->idx;
+
+	/*
+	 * For chained events, the low counter is programmed to count
+	 * the event of interest and the high counter is programmed
+	 * with CHAIN event code with filters set to count at all ELs.
+	 */
+	if (armv8pmu_event_is_chained(event)) {
+		u32 chain_evt = ARMV8_PMUV3_PERFCTR_CHAIN |
+				ARMV8_PMU_INCLUDE_EL2;
+
+		armv8pmu_write_evtype(idx - 1, hwc->config_base);
+		armv8pmu_write_evtype(idx, chain_evt);
+	} else {
+		armv8pmu_write_evtype(idx, hwc->config_base);
+	}
+}
+
 static inline int armv8pmu_enable_counter(int idx)
 {
 	u32 counter = ARMV8_IDX_TO_COUNTER(idx);
@@ -575,6 +644,16 @@ static inline int armv8pmu_enable_counter(int idx)
 	return idx;
 }
 
+static inline void armv8pmu_enable_event_counter(struct perf_event *event)
+{
+	int idx = event->hw.idx;
+
+	armv8pmu_enable_counter(idx);
+	if (armv8pmu_event_is_chained(event))
+		armv8pmu_enable_counter(idx - 1);
+	isb();
+}
+
 static inline int armv8pmu_disable_counter(int idx)
 {
 	u32 counter = ARMV8_IDX_TO_COUNTER(idx);
@@ -582,6 +661,16 @@ static inline int armv8pmu_disable_counter(int idx)
 	return idx;
 }
 
+static inline void armv8pmu_disable_event_counter(struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+	int idx = hwc->idx;
+
+	if (armv8pmu_event_is_chained(event))
+		armv8pmu_disable_counter(idx - 1);
+	armv8pmu_disable_counter(idx);
+}
+
 static inline int armv8pmu_enable_intens(int idx)
 {
 	u32 counter = ARMV8_IDX_TO_COUNTER(idx);
@@ -589,6 +678,11 @@ static inline int armv8pmu_enable_intens(int idx)
 	return idx;
 }
 
+static inline int armv8pmu_enable_event_irq(struct perf_event *event)
+{
+	return armv8pmu_enable_intens(event->hw.idx);
+}
+
 static inline int armv8pmu_disable_intens(int idx)
 {
 	u32 counter = ARMV8_IDX_TO_COUNTER(idx);
@@ -601,6 +695,11 @@ static inline int armv8pmu_disable_intens(int idx)
 	return idx;
 }
 
+static inline int armv8pmu_disable_event_irq(struct perf_event *event)
+{
+	return armv8pmu_disable_intens(event->hw.idx);
+}
+
 static inline u32 armv8pmu_getreset_flags(void)
 {
 	u32 value;
@@ -618,10 +717,8 @@ static inline u32 armv8pmu_getreset_flags(void)
 static void armv8pmu_enable_event(struct perf_event *event)
 {
 	unsigned long flags;
-	struct hw_perf_event *hwc = &event->hw;
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
 	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
-	int idx = hwc->idx;
 
 	/*
 	 * Enable counter and interrupt, and set the counter to count
@@ -632,22 +729,22 @@ static void armv8pmu_enable_event(struct perf_event *event)
 	/*
 	 * Disable counter
 	 */
-	armv8pmu_disable_counter(idx);
+	armv8pmu_disable_event_counter(event);
 
 	/*
 	 * Set event (if destined for PMNx counters).
 	 */
-	armv8pmu_write_evtype(idx, hwc->config_base);
+	armv8pmu_write_event_type(event);
 
 	/*
 	 * Enable interrupt for this counter
 	 */
-	armv8pmu_enable_intens(idx);
+	armv8pmu_enable_event_irq(event);
 
 	/*
 	 * Enable counter
 	 */
-	armv8pmu_enable_counter(idx);
+	armv8pmu_enable_event_counter(event);
 
 	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
@@ -655,10 +752,8 @@ static void armv8pmu_enable_event(struct perf_event *event)
 static void armv8pmu_disable_event(struct perf_event *event)
 {
 	unsigned long flags;
-	struct hw_perf_event *hwc = &event->hw;
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
 	struct pmu_hw_events *events = this_cpu_ptr(cpu_pmu->hw_events);
-	int idx = hwc->idx;
 
 	/*
 	 * Disable counter and interrupt
@@ -668,12 +763,12 @@ static void armv8pmu_disable_event(struct perf_event *event)
 	/*
 	 * Disable counter
 	 */
-	armv8pmu_disable_counter(idx);
+	armv8pmu_disable_event_counter(event);
 
 	/*
 	 * Disable interrupt for this counter
 	 */
-	armv8pmu_disable_intens(idx);
+	armv8pmu_disable_event_irq(event);
 
 	raw_spin_unlock_irqrestore(&events->pmu_lock, flags);
 }
@@ -767,10 +862,42 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
 	return IRQ_HANDLED;
 }
 
+static int armv8pmu_get_single_idx(struct pmu_hw_events *cpuc,
+				    struct arm_pmu *cpu_pmu)
+{
+	int idx;
+
+	for (idx = ARMV8_IDX_COUNTER0; idx < cpu_pmu->num_events; idx ++) {
+		if (!test_and_set_bit(idx, cpuc->used_mask))
+			return idx;
+	}
+	return -EAGAIN;
+}
+
+static int armv8pmu_get_chain_idx(struct pmu_hw_events *cpuc,
+				   struct arm_pmu *cpu_pmu)
+{
+	int idx;
+
+	/*
+	 * Chaining requires two consecutive event counters, where
+	 * the lower idx must be even.
+	 */
+	for (idx = ARMV8_IDX_COUNTER0 + 1; idx < cpu_pmu->num_events; idx += 2) {
+		if (!test_and_set_bit(idx, cpuc->used_mask)) {
+			/* Check if the preceding even counter is available */
+			if (!test_and_set_bit(idx - 1, cpuc->used_mask))
+				return idx;
+			/* Release the Odd counter */
+			clear_bit(idx, cpuc->used_mask);
+		}
+	}
+	return -EAGAIN;
+}
+
 static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 				  struct perf_event *event)
 {
-	int idx;
 	struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
 	struct hw_perf_event *hwc = &event->hw;
 	unsigned long evtype = hwc->config_base & ARMV8_PMU_EVTYPE_EVENT;
@@ -784,19 +911,20 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 	/*
 	 * Otherwise use events counters
 	 */
-	for (idx = ARMV8_IDX_COUNTER0; idx < cpu_pmu->num_events; ++idx) {
-		if (!test_and_set_bit(idx, cpuc->used_mask))
-			return idx;
-	}
-
-	/* The counters are all in use. */
-	return -EAGAIN;
+	if (armv8pmu_event_is_64bit(event))
+		return	armv8pmu_get_chain_idx(cpuc, cpu_pmu);
+	else
+		return armv8pmu_get_single_idx(cpuc, cpu_pmu);
 }
 
 static void armv8pmu_clear_event_idx(struct pmu_hw_events *cpuc,
-				  struct perf_event *event)
+				     struct perf_event *event)
 {
-	clear_bit(event->hw.idx, cpuc->used_mask);
+	int idx = event->hw.idx;
+
+	clear_bit(idx, cpuc->used_mask);
+	if (armv8pmu_event_is_chained(event))
+		clear_bit(idx - 1, cpuc->used_mask);
 }
 
 /*
@@ -871,6 +999,9 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
 				       &armv8_pmuv3_perf_cache_map,
 				       ARMV8_PMU_EVTYPE_EVENT);
 
+	if (armv8pmu_event_is_64bit(event))
+		event->hw.flags |= ARMPMU_EVT_64BIT;
+
 	/* Onl expose micro/arch events supported by this PMU */
 	if ((hw_event_id > 0) && (hw_event_id < ARMV8_PMUV3_MAX_COMMON_EVENTS)
 	    && test_bit(hw_event_id, armpmu->pmceid_bitmap)) {

drivers/perf/arm_pmu.c

@@ -665,14 +665,9 @@ static void cpu_pm_pmu_setup(struct arm_pmu *armpmu, unsigned long cmd)
 	int idx;
 
 	for (idx = 0; idx < armpmu->num_events; idx++) {
-		/*
-		 * If the counter is not used skip it, there is no
-		 * need of stopping/restarting it.
-		 */
-		if (!test_bit(idx, hw_events->used_mask))
-			continue;
-
 		event = hw_events->events[idx];
+		if (!event)
+			continue;
 
 		switch (cmd) {
 		case CPU_PM_ENTER: