[PATCH v7 14/16] perf python: Add evlist compute_metric

[Ian Rogers <irogers@google.com>]

Add a compute_metric function that computes a metric double value for a
given evlist, metric name, CPU and thread. For example:
```
>>> import perf
>>> x = perf.parse_metrics("TopdownL1")
>>> x.open()
>>> x.enable()
>>> x.disable()
>>> x.metrics()
['tma_bad_speculation', 'tma_frontend_bound', 'tma_backend_bound', 'tma_retiring']
>>> x.compute_metric('tma_bad_speculation', 0, -1)
0.08605342847131037
```

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/python.c | 125 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
index c1eab506f55b..980490684ab9 100644
--- a/tools/perf/util/python.c
+++ b/tools/perf/util/python.c
@@ -14,6 +14,7 @@
 #include "evlist.h"
 #include "evsel.h"
 #include "event.h"
+#include "expr.h"
 #include "print_binary.h"
 #include "record.h"
 #include "strbuf.h"
@@ -1320,6 +1321,124 @@ static PyObject *pyrf_evlist__metrics(struct pyrf_evlist *pevlist)
 	return list;
 }
 
+static int prepare_metric(const struct metric_expr *mexp,
+			  const struct evsel *evsel,
+			  struct expr_parse_ctx *pctx,
+			  int cpu_idx, int thread_idx)
+{
+	struct evsel * const *metric_events = mexp->metric_events;
+	struct metric_ref *metric_refs = mexp->metric_refs;
+
+	for (int i = 0; metric_events[i]; i++) {
+		char *n = strdup(evsel__metric_id(metric_events[i]));
+		double val, ena, run;
+		int source_count = evsel__source_count(metric_events[i]);
+		int ret;
+		struct perf_counts_values *old_count, *new_count;
+
+		if (!n)
+			return -ENOMEM;
+
+		if (source_count == 0)
+			source_count = 1;
+
+		ret = evsel__ensure_counts(metric_events[i]);
+		if (ret)
+			return ret;
+
+		/* Set up pointers to the old and newly read counter values. */
+		old_count = perf_counts(metric_events[i]->prev_raw_counts, cpu_idx, thread_idx);
+		new_count = perf_counts(metric_events[i]->counts, cpu_idx, thread_idx);
+		/* Update the value in metric_events[i]->counts. */
+		evsel__read_counter(metric_events[i], cpu_idx, thread_idx);
+
+		val = new_count->val - old_count->val;
+		ena = new_count->ena - old_count->ena;
+		run = new_count->run - old_count->run;
+
+		if (ena != run && run != 0)
+			val = val * ena / run;
+		ret = expr__add_id_val_source_count(pctx, n, val, source_count);
+		if (ret)
+			return ret;
+	}
+
+	for (int i = 0; metric_refs && metric_refs[i].metric_name; i++) {
+		int ret = expr__add_ref(pctx, &metric_refs[i]);
+
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static PyObject *pyrf_evlist__compute_metric(struct pyrf_evlist *pevlist,
+					     PyObject *args, PyObject *kwargs)
+{
+	int ret, cpu = 0, cpu_idx, thread = 0, thread_idx;
+	const char *metric;
+	struct rb_node *node;
+	struct metric_expr *mexp = NULL;
+	struct expr_parse_ctx *pctx;
+	double result = 0;
+
+	if (!PyArg_ParseTuple(args, "sii", &metric, &cpu, &thread))
+		return NULL;
+
+	for (node = rb_first_cached(&pevlist->evlist.metric_events.entries);
+	     mexp == NULL && node;
+	     node = rb_next(node)) {
+		struct metric_event *me = container_of(node, struct metric_event, nd);
+		struct list_head *pos;
+
+		list_for_each(pos, &me->head) {
+			struct metric_expr *e = container_of(pos, struct metric_expr, nd);
+
+			if (strcmp(e->metric_name, metric))
+				continue;
+
+			if (e->metric_events[0] == NULL)
+				continue;
+
+			cpu_idx = perf_cpu_map__idx(e->metric_events[0]->core.cpus,
+						    (struct perf_cpu){.cpu = cpu});
+			if (cpu_idx < 0)
+				continue;
+
+			thread_idx = perf_thread_map__idx(e->metric_events[0]->core.threads,
+							  thread);
+			if (thread_idx < 0)
+				continue;
+
+			mexp = e;
+			break;
+		}
+	}
+	if (!mexp) {
+		PyErr_Format(PyExc_TypeError, "Unknown metric '%s' for CPU '%d' and thread '%d'",
+			     metric, cpu, thread);
+		return NULL;
+	}
+
+	pctx = expr__ctx_new();
+	if (!pctx)
+		return PyErr_NoMemory();
+
+	ret = prepare_metric(mexp, mexp->metric_events[0], pctx, cpu_idx, thread_idx);
+	if (ret) {
+		expr__ctx_free(pctx);
+		errno = -ret;
+		PyErr_SetFromErrno(PyExc_OSError);
+		return NULL;
+	}
+	if (expr__parse(&result, pctx, mexp->metric_expr))
+		result = 0.0;
+
+	expr__ctx_free(pctx);
+	return PyFloat_FromDouble(result);
+}
+
 static PyObject *pyrf_evlist__mmap(struct pyrf_evlist *pevlist,
 				   PyObject *args, PyObject *kwargs)
 {
@@ -1554,6 +1673,12 @@ static PyMethodDef pyrf_evlist__methods[] = {
 		.ml_flags = METH_NOARGS,
 		.ml_doc	  = PyDoc_STR("List of metric names within the evlist.")
 	},
+	{
+		.ml_name  = "compute_metric",
+		.ml_meth  = (PyCFunction)pyrf_evlist__compute_metric,
+		.ml_flags = METH_VARARGS | METH_KEYWORDS,
+		.ml_doc	  = PyDoc_STR("compute metric for given name, cpu and thread")
+	},
 	{
 		.ml_name  = "mmap",
 		.ml_meth  = (PyCFunction)pyrf_evlist__mmap,
-- 
2.50.0.727.gbf7dc18ff4-goog