[PATCH 9/9] perf, tools: Update topdown documentation for Sapphire Rapids

kan.liang
2021-02-02T20:23:17Z

From: Kan Liang <kan.liang@linux.intel.com>

Update Topdown extension on Sapphire Rapids and how to collect the L2
events.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
---
tools/perf/Documentation/topdown.txt | 78 ++++++++++++++++++++++++++++++++++--
1 file changed, 74 insertions(+), 4 deletions(-)

diff --git a/tools/perf/Documentation/topdown.txt b/tools/perf/Documentation/topdown.txt
index 3c39bb3..10f07f9 100644
--- a/tools/perf/Documentation/topdown.txt
+++ b/tools/perf/Documentation/topdown.txt
@@ -121,7 +121,7 @@ to read slots and the topdown metrics at different points of the program:
#define RDPMC_METRIC (1 << 29) /* return metric counters */

#define FIXED_COUNTER_SLOTS 3
-#define METRIC_COUNTER_TOPDOWN_L1 0
+#define METRIC_COUNTER_TOPDOWN_L1_L2 0

static inline uint64_t read_slots(void)
{
@@ -130,7 +130,7 @@ static inline uint64_t read_slots(void)

static inline uint64_t read_metrics(void)
{
- return _rdpmc(RDPMC_METRIC | METRIC_COUNTER_TOPDOWN_L1);
+ return _rdpmc(RDPMC_METRIC | METRIC_COUNTER_TOPDOWN_L1_L2);
}

Then the program can be instrumented to read these metrics at different
@@ -152,11 +152,21 @@ The binary ratios in the metric value can be converted to float ratios:

#define GET_METRIC(m, i) (((m) >> (i*8)) & 0xff)

+/* L1 Topdown metric events */
#define TOPDOWN_RETIRING(val) ((float)GET_METRIC(val, 0) / 0xff)
#define TOPDOWN_BAD_SPEC(val) ((float)GET_METRIC(val, 1) / 0xff)
#define TOPDOWN_FE_BOUND(val) ((float)GET_METRIC(val, 2) / 0xff)
#define TOPDOWN_BE_BOUND(val) ((float)GET_METRIC(val, 3) / 0xff)

+/*
+ * L2 Topdown metric events.
+ * Available on Sapphire Rapids and later platforms.
+ */
+#define TOPDOWN_HEAVY_OPS(val) ((float)GET_METRIC(val, 4) / 0xff)
+#define TOPDOWN_BR_MISPREDICT(val) ((float)GET_METRIC(val, 5) / 0xff)
+#define TOPDOWN_FETCH_LAT(val) ((float)GET_METRIC(val, 6) / 0xff)
+#define TOPDOWN_MEM_BOUND(val) ((float)GET_METRIC(val, 7) / 0xff)
+
and then converted to percent for printing.

The ratios in the metric accumulate for the time when the counter
@@ -190,8 +200,8 @@ for that time period.
fe_bound_slots = GET_METRIC(metric_b, 2) * slots_b - fe_bound_slots_a
be_bound_slots = GET_METRIC(metric_b, 3) * slots_b - be_bound_slots_a

-Later the individual ratios for the measurement period can be recreated
-from these counts.
+Later the individual ratios of L1 metric events for the measurement period can
+be recreated from these counts.

slots_delta = slots_b - slots_a
retiring_ratio = (float)retiring_slots / slots_delta
@@ -205,6 +215,48 @@ from these counts.
fe_bound_ratio * 100.,
be_bound_ratio * 100.);

+The individual ratios of L2 metric events for the measurement period can be
+recreated from L1 and L2 metric counters. (Available on Sapphire Rapids and
+later platforms)
+
+ # compute scaled metrics for measurement a
+ heavy_ops_slots_a = GET_METRIC(metric_a, 4) * slots_a
+ br_mispredict_slots_a = GET_METRIC(metric_a, 5) * slots_a
+ fetch_lat_slots_a = GET_METRIC(metric_a, 6) * slots_a
+ mem_bound_slots_a = GET_METRIC(metric_a, 7) * slots_a
+
+ # compute delta scaled metrics between b and a
+ heavy_ops_slots = GET_METRIC(metric_b, 4) * slots_b - heavy_ops_slots_a
+ br_mispredict_slots = GET_METRIC(metric_b, 5) * slots_b - br_mispredict_slots_a
+ fetch_lat_slots = GET_METRIC(metric_b, 6) * slots_b - fetch_lat_slots_a
+ mem_bound_slots = GET_METRIC(metric_b, 7) * slots_b - mem_bound_slots_a
+
+ slots_delta = slots_b - slots_a
+ heavy_ops_ratio = (float)heavy_ops_slots / slots_delta
+ light_ops_ratio = retiring_ratio - heavy_ops_ratio;
+
+ br_mispredict_ratio = (float)br_mispredict_slots / slots_delta
+ machine_clears_ratio = bad_spec_ratio - br_mispredict_ratio;
+
+ fetch_lat_ratio = (float)fetch_lat_slots / slots_delta
+ fetch_bw_ratio = fe_bound_ratio - fetch_lat_ratio;
+
+ mem_bound_ratio = (float)mem_bound_slots / slota_delta
+ core_bound_ratio = be_bound_ratio - mem_bound_ratio;
+
+ printf("Heavy Operations %.2f%% Light Operations %.2f%% "
+ "Branch Mispredict %.2f%% Machine Clears %.2f%% "
+ "Fetch Latency %.2f%% Fetch Bandwidth %.2f%% "
+ "Mem Bound %.2f%% Core Bound %.2f%%\n",
+ heavy_ops_ratio * 100.,
+ light_ops_ratio * 100.,
+ br_mispredict_ratio * 100.,
+ machine_clears_ratio * 100.,
+ fetch_lat_ratio * 100.,
+ fetch_bw_ratio * 100.,
+ mem_bound_ratio * 100.,
+ core_bound_ratio * 100.);
+
Resetting metrics counters
==========================

@@ -248,6 +300,24 @@ a sampling read group. Since the SLOTS event must be the leader of a TopDown
group, the second event of the group is the sampling event.
For example, perf record -e '{slots, $sampling_event, topdown-retiring}:S'

+Extension on Sapphire Rapids Server
+===================================
+The metrics counter is extended to support TMA method level 2 metrics.
+The lower half of the register is the TMA level 1 metrics (legacy).
+The upper half is also divided into four 8-bit fields for the new level 2
+metrics. Four more TopDown metric events are exposed for the end-users,
+topdown-heavy-ops, topdown-br-mispredict, topdown-fetch-lat and
+topdown-mem-bound.
+
+Each of the new level 2 metrics in the upper half is a subset of the
+corresponding level 1 metric in the lower half. Software can deduce the
+other four level 2 metrics by subtracting corresponding metrics as below.
+
+ Light_Operations = Retiring - Heavy_Operations
+ Machine_Clears = Bad_Speculation - Branch_Mispredicts
+ Fetch_Bandwidth = Frontend_Bound - Fetch_Latency
+ Core_Bound = Backend_Bound - Memory_Bound
+

[1] https://software.intel.com/en-us/top-down-microarchitecture-analysis-method-win
[2] https://github.com/andikleen/pmu-tools/wiki/toplev-manual
--
2.7.4