[PATCH 06/10] perf, tools, stat: Add computation of TopDown formulas

Andi Kleen
2015-12-16T00:56:37Z

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.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
tools/perf/builtin-stat.c | 6 +-
tools/perf/util/stat-shadow.c | 164 +++++++++++++++++++++++++++++++++++++++++-
tools/perf/util/stat.c | 5 ++
tools/perf/util/stat.h | 8 ++-
4 files changed, 179 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index e10198c..6c44aae 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -859,7 +859,8 @@ static void printout(int id, int nr, struct perf_evsel *counter, double uval,
perf_stat__print_shadow_stats(counter, uval,
stat_config.aggr_mode == AGGR_GLOBAL ? 0 :
first_shadow_cpu(counter, id),
- &out);
+ &out,
+ topdown_run);

if (!metric_only) {
print_noise(counter, noise);
@@ -1048,7 +1049,8 @@ static void print_metric_headers(char *prefix)
os.evsel = counter;
perf_stat__print_shadow_stats(counter, 0,
0,
- &out);
+ &out,
+ topdown_run);
}
fputc('\n', stat_config.output);
}
diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
index 4d8f185..e977992 100644
--- a/tools/perf/util/stat-shadow.c
+++ b/tools/perf/util/stat-shadow.c
@@ -2,6 +2,7 @@
#include "evsel.h"
#include "stat.h"
#include "color.h"
+#include "pmu.h"

enum {
CTX_BIT_USER = 1 << 0,
@@ -28,6 +29,11 @@ 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];

struct stats walltime_nsecs_stats;

@@ -68,6 +74,11 @@ 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));
}

/*
@@ -90,6 +101,16 @@ 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))
@@ -289,9 +310,108 @@ 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 .agg-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)
+ struct perf_stat_output_ctx *out,
+ int topdown_run)
{
void *ctxp = out->ctx;
print_metric_t print_metric = out->print_metric;
@@ -438,6 +558,48 @@ 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 || topdown_run > 1)
+ print_metric(ctxp, NULL, "%8.2f%%", "frontend bound",
+ fe_bound * 100.);
+ else
+ print_metric(ctxp, NULL, NULL, "frontend bound", 0);
+ } else if (perf_stat_evsel__is(evsel, TOPDOWN_SLOTS_RETIRED)) {
+ double retiring = td_retiring(ctx, cpu);
+
+ if (retiring > 0.7 || topdown_run > 1)
+ print_metric(ctxp, NULL, "%8.2f%%", "retiring",
+ retiring * 100.);
+ else
+ print_metric(ctxp, NULL, NULL, "retiring", 0);
+ } else if (perf_stat_evsel__is(evsel, TOPDOWN_RECOVERY_BUBBLES)) {
+ double bad_spec = td_bad_spec(ctx, cpu);
+
+ if (bad_spec > 0.1 || topdown_run > 1)
+ print_metric(ctxp, NULL, "%8.2f%%", "bad speculation",
+ bad_spec * 100.);
+ else
+ print_metric(ctxp, NULL, NULL, "bad speculation", 0);
+ } 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 (td_total_slots(ctx, cpu) > 0 &&
+ (be_bound > 0.2 || topdown_run > 1))
+ print_metric(ctxp, NULL, "%8.2f%%", 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 913d236..fdb34e3 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 f51d94e..0c26633 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,
};

@@ -83,7 +88,8 @@ struct perf_stat_output_ctx {

void perf_stat__print_shadow_stats(struct perf_evsel *evsel,
double avg, int cpu,
- struct perf_stat_output_ctx *out);
+ struct perf_stat_output_ctx *out,
+ int topdown_run);

void perf_evsel__reset_stat_priv(struct perf_evsel *evsel);
int perf_evsel__alloc_stat_priv(struct perf_evsel *evsel);
--
2.4.3