perf/x86/intel: Generic support for hardware TopDown metrics

Intro
=====

The TopDown Microarchitecture Analysis (TMA) Method is a structured
analysis methodology to identify critical performance bottlenecks in
out-of-order processors. Current perf has supported the method.

The method works well, but there is one problem. To collect the TopDown
events, several GP counters have to be used. If a user wants to collect
other events at the same time, the multiplexing probably be triggered,
which impacts the accuracy.

To free up the scarce GP counters, the hardware TopDown metrics feature
is introduced from Ice Lake. The hardware implements an additional
"metrics" register and a new Fixed Counter 3 that measures pipeline
"slots". The TopDown events can be calculated from them instead.

Events
======

The level 1 TopDown has four metrics. There is no event-code assigned to
the TopDown metrics. Four metric events are exported as separate perf
events, which map to the internal "metrics" counter register. Those
events do not exist in hardware, but can be allocated by the scheduler.

For the event mapping, a special 0x00 event code is used, which is
reserved for fake events. The metric events start from umask 0x10.

When setting up the metric events, they point to the Fixed Counter 3.
They have to be specially handled.
- Add the update_topdown_event() callback to read the additional metrics
  MSR and generate the metrics.
- Add the set_topdown_event_period() callback to initialize metrics MSR
  and the fixed counter 3.
- Add a variable n_metric_event to track the number of the accepted
  metrics events. The sharing between multiple users of the same metric
  without multiplexing is not allowed.
- Only enable/disable the fixed counter 3 when there are no other active
  TopDown events, which avoid the unnecessary writing of the fixed
  control register.
- Disable the PMU when reading the metrics event. The metrics MSR and
  the fixed counter 3 are read separately. The values may be modified by
  an NMI.

All four metric events don't support sampling. Since they will be
handled specially for event update, a flag PERF_X86_EVENT_TOPDOWN is
introduced to indicate this case.

The slots event can support both sampling and counting.
For counting, the flag is also applied.
For sampling, it will be handled normally as other normal events.

Groups
======

The slots event is required in a Topdown group.
To avoid reading the METRICS register multiple times, the metrics and
slots value can only be updated by slots event in a group.
All active slots and metrics events will be updated one time.
Therefore, the slots event must be before any metric events in a Topdown
group.

NMI
======

The METRICS related register may be overflow. The bit 48 of the STATUS
register will be set. If so, PERF_METRICS and Fixed counter 3 are
required to be reset. The patch also update all active slots and
metrics events in the NMI handler.

The update_topdown_event() has to read two registers separately. The
values may be modified by an NMI. PMU has to be disabled before calling
the function.

RDPMC
======

RDPMC is temporarily disabled. A later patch will enable it.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200723171117.9918-9-kan.liang@linux.intel.com

1 files changed, 119 insertions, 5 deletions

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 76eab8178047..4a436681f6ea 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2165,11 +2165,24 @@ static inline void intel_clear_masks(struct perf_event *event, int idx)
 static void intel_pmu_disable_fixed(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
-	int idx = hwc->idx - INTEL_PMC_IDX_FIXED;
 	u64 ctrl_val, mask;
+	int idx = hwc->idx;
 
-	mask = 0xfULL << (idx * 4);
+	if (is_topdown_idx(idx)) {
+		struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+		/*
+		 * When there are other active TopDown events,
+		 * don't disable the fixed counter 3.
+		 */
+		if (*(u64 *)cpuc->active_mask & INTEL_PMC_OTHER_TOPDOWN_BITS(idx))
+			return;
+		idx = INTEL_PMC_IDX_FIXED_SLOTS;
+	}
 
+	intel_clear_masks(event, idx);
+
+	mask = 0xfULL << ((idx - INTEL_PMC_IDX_FIXED) * 4);
 	rdmsrl(hwc->config_base, ctrl_val);
 	ctrl_val &= ~mask;
 	wrmsrl(hwc->config_base, ctrl_val);
@@ -2186,7 +2199,7 @@ static void intel_pmu_disable_event(struct perf_event *event)
 		x86_pmu_disable_event(event);
 		break;
 	case INTEL_PMC_IDX_FIXED ... INTEL_PMC_IDX_FIXED_BTS - 1:
-		intel_clear_masks(event, idx);
+	case INTEL_PMC_IDX_METRIC_BASE ... INTEL_PMC_IDX_METRIC_END:
 		intel_pmu_disable_fixed(event);
 		break;
 	case INTEL_PMC_IDX_FIXED_BTS:
@@ -2219,10 +2232,26 @@ static void intel_pmu_del_event(struct perf_event *event)
 		intel_pmu_pebs_del(event);
 }
 
+static void intel_pmu_read_topdown_event(struct perf_event *event)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	/* Only need to call update_topdown_event() once for group read. */
+	if ((cpuc->txn_flags & PERF_PMU_TXN_READ) &&
+	    !is_slots_event(event))
+		return;
+
+	perf_pmu_disable(event->pmu);
+	x86_pmu.update_topdown_event(event);
+	perf_pmu_enable(event->pmu);
+}
+
 static void intel_pmu_read_event(struct perf_event *event)
 {
 	if (event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)
 		intel_pmu_auto_reload_read(event);
+	else if (is_topdown_count(event) && x86_pmu.update_topdown_event)
+		intel_pmu_read_topdown_event(event);
 	else
 		x86_perf_event_update(event);
 }
@@ -2230,8 +2259,22 @@ static void intel_pmu_read_event(struct perf_event *event)
 static void intel_pmu_enable_fixed(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
-	int idx = hwc->idx - INTEL_PMC_IDX_FIXED;
 	u64 ctrl_val, mask, bits = 0;
+	int idx = hwc->idx;
+
+	if (is_topdown_idx(idx)) {
+		struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+		/*
+		 * When there are other active TopDown events,
+		 * don't enable the fixed counter 3 again.
+		 */
+		if (*(u64 *)cpuc->active_mask & INTEL_PMC_OTHER_TOPDOWN_BITS(idx))
+			return;
+
+		idx = INTEL_PMC_IDX_FIXED_SLOTS;
+	}
+
+	intel_set_masks(event, idx);
 
 	/*
 	 * Enable IRQ generation (0x8), if not PEBS,
@@ -2251,6 +2294,7 @@ static void intel_pmu_enable_fixed(struct perf_event *event)
 	if (x86_pmu.version > 2 && hwc->config & ARCH_PERFMON_EVENTSEL_ANY)
 		bits |= 0x4;
 
+	idx -= INTEL_PMC_IDX_FIXED;
 	bits <<= (idx * 4);
 	mask = 0xfULL << (idx * 4);
 
@@ -2279,7 +2323,7 @@ static void intel_pmu_enable_event(struct perf_event *event)
 		__x86_pmu_enable_event(hwc, ARCH_PERFMON_EVENTSEL_ENABLE);
 		break;
 	case INTEL_PMC_IDX_FIXED ... INTEL_PMC_IDX_FIXED_BTS - 1:
-		intel_set_masks(event, idx);
+	case INTEL_PMC_IDX_METRIC_BASE ... INTEL_PMC_IDX_METRIC_END:
 		intel_pmu_enable_fixed(event);
 		break;
 	case INTEL_PMC_IDX_FIXED_BTS:
@@ -2440,6 +2484,15 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
 	}
 
 	/*
+	 * Intel Perf mertrics
+	 */
+	if (__test_and_clear_bit(GLOBAL_STATUS_PERF_METRICS_OVF_BIT, (unsigned long *)&status)) {
+		handled++;
+		if (x86_pmu.update_topdown_event)
+			x86_pmu.update_topdown_event(NULL);
+	}
+
+	/*
 	 * Checkpointed counters can lead to 'spurious' PMIs because the
 	 * rollback caused by the PMI will have cleared the overflow status
 	 * bit. Therefore always force probe these counters.
@@ -3375,6 +3428,58 @@ static int intel_pmu_hw_config(struct perf_event *event)
 	if (event->attr.type != PERF_TYPE_RAW)
 		return 0;
 
+	/*
+	 * Config Topdown slots and metric events
+	 *
+	 * The slots event on Fixed Counter 3 can support sampling,
+	 * which will be handled normally in x86_perf_event_update().
+	 *
+	 * Metric events don't support sampling and require being paired
+	 * with a slots event as group leader. When the slots event
+	 * is used in a metrics group, it too cannot support sampling.
+	 */
+	if (x86_pmu.intel_cap.perf_metrics && is_topdown_event(event)) {
+		if (event->attr.config1 || event->attr.config2)
+			return -EINVAL;
+
+		/*
+		 * The TopDown metrics events and slots event don't
+		 * support any filters.
+		 */
+		if (event->attr.config & X86_ALL_EVENT_FLAGS)
+			return -EINVAL;
+
+		if (is_metric_event(event)) {
+			struct perf_event *leader = event->group_leader;
+
+			/* The metric events don't support sampling. */
+			if (is_sampling_event(event))
+				return -EINVAL;
+
+			/* The metric events require a slots group leader. */
+			if (!is_slots_event(leader))
+				return -EINVAL;
+
+			/*
+			 * The leader/SLOTS must not be a sampling event for
+			 * metric use; hardware requires it starts at 0 when used
+			 * in conjunction with MSR_PERF_METRICS.
+			 */
+			if (is_sampling_event(leader))
+				return -EINVAL;
+
+			event->event_caps |= PERF_EV_CAP_SIBLING;
+			/*
+			 * Only once we have a METRICs sibling do we
+			 * need TopDown magic.
+			 */
+			leader->hw.flags |= PERF_X86_EVENT_TOPDOWN;
+			event->hw.flags  |= PERF_X86_EVENT_TOPDOWN;
+
+			event->hw.flags &= ~PERF_X86_EVENT_RDPMC_ALLOWED;
+		}
+	}
+
 	if (!(event->attr.config & ARCH_PERFMON_EVENTSEL_ANY))
 		return 0;
 
@@ -5218,6 +5323,15 @@ __init int intel_pmu_init(void)
 		 * counter, so do not extend mask to generic counters
 		 */
 		for_each_event_constraint(c, x86_pmu.event_constraints) {
+			/*
+			 * Don't extend the topdown slots and metrics
+			 * events to the generic counters.
+			 */
+			if (c->idxmsk64 & INTEL_PMC_MSK_TOPDOWN) {
+				c->weight = hweight64(c->idxmsk64);
+				continue;
+			}
+
 			if (c->cmask == FIXED_EVENT_FLAGS
 			    && c->idxmsk64 != INTEL_PMC_MSK_FIXED_REF_CYCLES) {
 				c->idxmsk64 |= (1ULL << x86_pmu.num_counters) - 1;