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, 47 insertions, 0 deletions

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 58419e50ff98..000cab7818b5 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -244,6 +244,52 @@ struct x86_pmu_capability {
  */
 #define INTEL_PMC_IDX_FIXED_BTS			(INTEL_PMC_IDX_FIXED + 15)
 
+/*
+ * The PERF_METRICS MSR is modeled as several magic fixed-mode PMCs, one for
+ * each TopDown metric event.
+ *
+ * Internally the TopDown metric events are mapped to the FxCtr 3 (SLOTS).
+ */
+#define INTEL_PMC_IDX_METRIC_BASE		(INTEL_PMC_IDX_FIXED + 16)
+#define INTEL_PMC_IDX_TD_RETIRING		(INTEL_PMC_IDX_METRIC_BASE + 0)
+#define INTEL_PMC_IDX_TD_BAD_SPEC		(INTEL_PMC_IDX_METRIC_BASE + 1)
+#define INTEL_PMC_IDX_TD_FE_BOUND		(INTEL_PMC_IDX_METRIC_BASE + 2)
+#define INTEL_PMC_IDX_TD_BE_BOUND		(INTEL_PMC_IDX_METRIC_BASE + 3)
+#define INTEL_PMC_IDX_METRIC_END		INTEL_PMC_IDX_TD_BE_BOUND
+#define INTEL_PMC_MSK_TOPDOWN			((0xfull << INTEL_PMC_IDX_METRIC_BASE) | \
+						INTEL_PMC_MSK_FIXED_SLOTS)
+
+/*
+ * There is no event-code assigned to the TopDown events.
+ *
+ * For the slots event, use the pseudo code of the fixed counter 3.
+ *
+ * For the metric events, the pseudo event-code is 0x00.
+ * The pseudo umask-code starts from the middle of the pseudo event
+ * space, 0x80.
+ */
+#define INTEL_TD_SLOTS				0x0400	/* TOPDOWN.SLOTS */
+/* Level 1 metrics */
+#define INTEL_TD_METRIC_RETIRING		0x8000	/* Retiring metric */
+#define INTEL_TD_METRIC_BAD_SPEC		0x8100	/* Bad speculation metric */
+#define INTEL_TD_METRIC_FE_BOUND		0x8200	/* FE bound metric */
+#define INTEL_TD_METRIC_BE_BOUND		0x8300	/* BE bound metric */
+#define INTEL_TD_METRIC_MAX			INTEL_TD_METRIC_BE_BOUND
+#define INTEL_TD_METRIC_NUM			4
+
+static inline bool is_metric_idx(int idx)
+{
+	return (unsigned)(idx - INTEL_PMC_IDX_METRIC_BASE) < INTEL_TD_METRIC_NUM;
+}
+
+static inline bool is_topdown_idx(int idx)
+{
+	return is_metric_idx(idx) || idx == INTEL_PMC_IDX_FIXED_SLOTS;
+}
+
+#define INTEL_PMC_OTHER_TOPDOWN_BITS(bit)	\
+			(~(0x1ull << bit) & INTEL_PMC_MSK_TOPDOWN)
+
 #define GLOBAL_STATUS_COND_CHG			BIT_ULL(63)
 #define GLOBAL_STATUS_BUFFER_OVF_BIT		62
 #define GLOBAL_STATUS_BUFFER_OVF		BIT_ULL(GLOBAL_STATUS_BUFFER_OVF_BIT)
@@ -254,6 +300,7 @@ struct x86_pmu_capability {
 #define GLOBAL_STATUS_LBRS_FROZEN		BIT_ULL(GLOBAL_STATUS_LBRS_FROZEN_BIT)
 #define GLOBAL_STATUS_TRACE_TOPAPMI_BIT		55
 #define GLOBAL_STATUS_TRACE_TOPAPMI		BIT_ULL(GLOBAL_STATUS_TRACE_TOPAPMI_BIT)
+#define GLOBAL_STATUS_PERF_METRICS_OVF_BIT	48
 
 /*
  * We model guest LBR event tracing as another fixed-mode PMC like BTS.