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Subject[PATCH 10/11] perf, tools, stat: Add computation of TopDown formulas
Date
From: Andi Kleen <ak@linux.intel.com>

Implement the TopDown formulas in perf stat. The topdown basic metrics
reported by the kernel are collected, and the formulas are computed
and output as normal metrics.

See the kernel commit exporting the events for details on the used
metrics.

v2: Always print all metrics, only use thresholds for coloring.
v3: Mark retiring over threshold green, not red.
v4:
Only print one decimal digit
Fix color printing of one metric
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
tools/perf/util/stat-shadow.c | 160 ++++++++++++++++++++++++++++++++++++++++++
tools/perf/util/stat.c | 5 ++
tools/perf/util/stat.h | 5 ++
3 files changed, 170 insertions(+)

diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
index fdb71961143e..deb4a33acf1e 100644
--- a/tools/perf/util/stat-shadow.c
+++ b/tools/perf/util/stat-shadow.c
@@ -36,6 +36,11 @@ static struct stats runtime_dtlb_cache_stats[NUM_CTX][MAX_NR_CPUS];
static struct stats runtime_cycles_in_tx_stats[NUM_CTX][MAX_NR_CPUS];
static struct stats runtime_transaction_stats[NUM_CTX][MAX_NR_CPUS];
static struct stats runtime_elision_stats[NUM_CTX][MAX_NR_CPUS];
+static struct stats runtime_topdown_total_slots[NUM_CTX][MAX_NR_CPUS];
+static struct stats runtime_topdown_slots_issued[NUM_CTX][MAX_NR_CPUS];
+static struct stats runtime_topdown_slots_retired[NUM_CTX][MAX_NR_CPUS];
+static struct stats runtime_topdown_fetch_bubbles[NUM_CTX][MAX_NR_CPUS];
+static struct stats runtime_topdown_recovery_bubbles[NUM_CTX][MAX_NR_CPUS];
static bool have_frontend_stalled;

struct stats walltime_nsecs_stats;
@@ -82,6 +87,12 @@ void perf_stat__reset_shadow_stats(void)
sizeof(runtime_transaction_stats));
memset(runtime_elision_stats, 0, sizeof(runtime_elision_stats));
memset(&walltime_nsecs_stats, 0, sizeof(walltime_nsecs_stats));
+ memset(runtime_topdown_total_slots, 0, sizeof(runtime_topdown_total_slots));
+ memset(runtime_topdown_slots_retired, 0, sizeof(runtime_topdown_slots_retired));
+ memset(runtime_topdown_slots_issued, 0, sizeof(runtime_topdown_slots_issued));
+ memset(runtime_topdown_fetch_bubbles, 0, sizeof(runtime_topdown_fetch_bubbles));
+ memset(runtime_topdown_recovery_bubbles, 0, sizeof(runtime_topdown_recovery_bubbles));
+ have_frontend_stalled = pmu_have_event("cpu", "stalled-cycles-frontend");
}

/*
@@ -104,6 +115,16 @@ void perf_stat__update_shadow_stats(struct perf_evsel *counter, u64 *count,
update_stats(&runtime_transaction_stats[ctx][cpu], count[0]);
else if (perf_stat_evsel__is(counter, ELISION_START))
update_stats(&runtime_elision_stats[ctx][cpu], count[0]);
+ else if (perf_stat_evsel__is(counter, TOPDOWN_TOTAL_SLOTS))
+ update_stats(&runtime_topdown_total_slots[ctx][cpu], count[0]);
+ else if (perf_stat_evsel__is(counter, TOPDOWN_SLOTS_ISSUED))
+ update_stats(&runtime_topdown_slots_issued[ctx][cpu], count[0]);
+ else if (perf_stat_evsel__is(counter, TOPDOWN_SLOTS_RETIRED))
+ update_stats(&runtime_topdown_slots_retired[ctx][cpu], count[0]);
+ else if (perf_stat_evsel__is(counter, TOPDOWN_FETCH_BUBBLES))
+ update_stats(&runtime_topdown_fetch_bubbles[ctx][cpu],count[0]);
+ else if (perf_stat_evsel__is(counter, TOPDOWN_RECOVERY_BUBBLES))
+ update_stats(&runtime_topdown_recovery_bubbles[ctx][cpu], count[0]);
else if (perf_evsel__match(counter, HARDWARE, HW_STALLED_CYCLES_FRONTEND))
update_stats(&runtime_stalled_cycles_front_stats[ctx][cpu], count[0]);
else if (perf_evsel__match(counter, HARDWARE, HW_STALLED_CYCLES_BACKEND))
@@ -301,6 +322,104 @@ static void print_ll_cache_misses(int cpu,
out->print_metric(out->ctx, color, "%7.2f%%", "of all LL-cache hits", ratio);
}

+/*
+ * High level "TopDown" CPU core pipe line bottleneck break down.
+ *
+ * Basic concept following
+ * Yasin, A Top Down Method for Performance analysis and Counter architecture
+ * ISPASS14
+ *
+ * The CPU pipeline is divided into 4 areas that can be bottlenecks:
+ *
+ * Frontend -> Backend -> Retiring
+ * BadSpeculation in addition means out of order execution that is thrown away
+ * (for example branch mispredictions)
+ * Frontend is instruction decoding.
+ * Backend is execution, like computation and accessing data in memory
+ * Retiring is good execution that is not directly bottlenecked
+ *
+ * The formulas are computed in slots.
+ * A slot is an entry in the pipeline each for the pipeline width
+ * (for example a 4-wide pipeline has 4 slots for each cycle)
+ *
+ * Formulas:
+ * BadSpeculation = ((SlotsIssued - SlotsRetired) + RecoveryBubbles) /
+ * TotalSlots
+ * Retiring = SlotsRetired / TotalSlots
+ * FrontendBound = FetchBubbles / TotalSlots
+ * BackendBound = 1.0 - BadSpeculation - Retiring - FrontendBound
+ *
+ * The kernel provides the mapping to the low level CPU events and any scaling
+ * needed for the CPU pipeline width, for example:
+ *
+ * TotalSlots = Cycles * 4
+ *
+ * The scaling factor is communicated in the sysfs unit.
+ *
+ * In some cases the CPU may not be able to measure all the formulas due to
+ * missing events. In this case multiple formulas are combined, as possible.
+ *
+ * With SMT the slots of thread siblings need to be combined to get meaningful
+ * results. This is implemented by the kernel forcing per-core mode with
+ * the .aggr-per-core sysfs attribute.
+ *
+ * Full TopDown supports more levels to sub-divide each area: for example
+ * BackendBound into computing bound and memory bound. For now we only
+ * support Level 1 TopDown.
+ */
+
+static double td_total_slots(int ctx, int cpu)
+{
+ return avg_stats(&runtime_topdown_total_slots[ctx][cpu]);
+}
+
+static double td_bad_spec(int ctx, int cpu)
+{
+ double bad_spec = 0;
+ double total_slots;
+ double total;
+
+ total = avg_stats(&runtime_topdown_slots_issued[ctx][cpu]) -
+ avg_stats(&runtime_topdown_slots_retired[ctx][cpu]) +
+ avg_stats(&runtime_topdown_recovery_bubbles[ctx][cpu]);
+ total_slots = td_total_slots(ctx, cpu);
+ if (total_slots)
+ bad_spec = total / total_slots;
+ return bad_spec;
+}
+
+static double td_retiring(int ctx, int cpu)
+{
+ double retiring = 0;
+ double total_slots = td_total_slots(ctx, cpu);
+ double ret_slots = avg_stats(&runtime_topdown_slots_retired[ctx][cpu]);
+
+ if (total_slots)
+ retiring = ret_slots / total_slots;
+ return retiring;
+}
+
+static double td_fe_bound(int ctx, int cpu)
+{
+ double fe_bound = 0;
+ double total_slots = td_total_slots(ctx, cpu);
+ double fetch_bub = avg_stats(&runtime_topdown_fetch_bubbles[ctx][cpu]);
+
+ if (total_slots)
+ fe_bound = fetch_bub / total_slots;
+ return fe_bound;
+}
+
+static double td_be_bound(int ctx, int cpu)
+{
+ double sum = (td_fe_bound(ctx, cpu) +
+ td_bad_spec(ctx, cpu) +
+ td_retiring(ctx, cpu));
+ if (sum == 0)
+ return 0;
+ return 1.0 - sum;
+}
+
void perf_stat__print_shadow_stats(struct perf_evsel *evsel,
double avg, int cpu,
struct perf_stat_output_ctx *out)
@@ -308,6 +427,7 @@ void perf_stat__print_shadow_stats(struct perf_evsel *evsel,
void *ctxp = out->ctx;
print_metric_t print_metric = out->print_metric;
double total, ratio = 0.0, total2;
+ const char *color = NULL;
int ctx = evsel_context(evsel);

if (perf_evsel__match(evsel, HARDWARE, HW_INSTRUCTIONS)) {
@@ -450,6 +570,46 @@ void perf_stat__print_shadow_stats(struct perf_evsel *evsel,
avg / ratio);
else
print_metric(ctxp, NULL, NULL, "CPUs utilized", 0);
+ } else if (perf_stat_evsel__is(evsel, TOPDOWN_FETCH_BUBBLES)) {
+ double fe_bound = td_fe_bound(ctx, cpu);
+
+ if (fe_bound > 0.2)
+ color = PERF_COLOR_RED;
+ print_metric(ctxp, color, "%8.1f%%", "frontend bound",
+ fe_bound * 100.);
+ } else if (perf_stat_evsel__is(evsel, TOPDOWN_SLOTS_RETIRED)) {
+ double retiring = td_retiring(ctx, cpu);
+
+ if (retiring > 0.7)
+ color = PERF_COLOR_GREEN;
+ print_metric(ctxp, color, "%8.1f%%", "retiring",
+ retiring * 100.);
+ } else if (perf_stat_evsel__is(evsel, TOPDOWN_RECOVERY_BUBBLES)) {
+ double bad_spec = td_bad_spec(ctx, cpu);
+
+ if (bad_spec > 0.1)
+ color = PERF_COLOR_RED;
+ print_metric(ctxp, color, "%8.1f%%", "bad speculation",
+ bad_spec * 100.);
+ } else if (perf_stat_evsel__is(evsel, TOPDOWN_SLOTS_ISSUED)) {
+ double be_bound = td_be_bound(ctx, cpu);
+ const char *name = "backend bound";
+ static int have_recovery_bubbles = -1;
+
+ /* In case the CPU does not support topdown-recovery-bubbles */
+ if (have_recovery_bubbles < 0)
+ have_recovery_bubbles = pmu_have_event("cpu",
+ "topdown-recovery-bubbles");
+ if (!have_recovery_bubbles)
+ name = "backend bound/bad spec";
+
+ if (be_bound > 0.2)
+ color = PERF_COLOR_RED;
+ if (td_total_slots(ctx, cpu) > 0)
+ print_metric(ctxp, color, "%8.1f%%", name,
+ be_bound * 100.);
+ else
+ print_metric(ctxp, NULL, NULL, name, 0);
} else if (runtime_nsecs_stats[cpu].n != 0) {
char unit = 'M';
char unit_buf[10];
diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
index ffa1d0653861..c1ba255f2abe 100644
--- a/tools/perf/util/stat.c
+++ b/tools/perf/util/stat.c
@@ -79,6 +79,11 @@ static const char *id_str[PERF_STAT_EVSEL_ID__MAX] = {
ID(TRANSACTION_START, cpu/tx-start/),
ID(ELISION_START, cpu/el-start/),
ID(CYCLES_IN_TX_CP, cpu/cycles-ct/),
+ ID(TOPDOWN_TOTAL_SLOTS, topdown-total-slots),
+ ID(TOPDOWN_SLOTS_ISSUED, topdown-slots-issued),
+ ID(TOPDOWN_SLOTS_RETIRED, topdown-slots-retired),
+ ID(TOPDOWN_FETCH_BUBBLES, topdown-fetch-bubbles),
+ ID(TOPDOWN_RECOVERY_BUBBLES, topdown-recovery-bubbles),
};
#undef ID

diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h
index 0150e786ccc7..c29bb94c48a4 100644
--- a/tools/perf/util/stat.h
+++ b/tools/perf/util/stat.h
@@ -17,6 +17,11 @@ enum perf_stat_evsel_id {
PERF_STAT_EVSEL_ID__TRANSACTION_START,
PERF_STAT_EVSEL_ID__ELISION_START,
PERF_STAT_EVSEL_ID__CYCLES_IN_TX_CP,
+ PERF_STAT_EVSEL_ID__TOPDOWN_TOTAL_SLOTS,
+ PERF_STAT_EVSEL_ID__TOPDOWN_SLOTS_ISSUED,
+ PERF_STAT_EVSEL_ID__TOPDOWN_SLOTS_RETIRED,
+ PERF_STAT_EVSEL_ID__TOPDOWN_FETCH_BUBBLES,
+ PERF_STAT_EVSEL_ID__TOPDOWN_RECOVERY_BUBBLES,
PERF_STAT_EVSEL_ID__MAX,
};

--
2.5.5
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