perf test: Make metric testing more robust

When testing metric expressions we fake counter values from 1 going
upward. For some metrics this can yield negative values that are clipped
to zero, and then cause divide by zero failures.

Such clipping is questionable but may be a result of tools automatically
generating metrics. A workaround for this case is to try a second time
with counter values going in the opposite direction.

This case was seen in a metric like:
  event1 / max(event2 - event3, 0)
But it may also happen in more sensible metrics like:
  event1 / (event2 + event3 - 1 - event4)

Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211223185622.3435128-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/pmu-events.c

@@ -994,8 +994,18 @@ static int test__parsing(struct test_suite *test __maybe_unused,
 			}
 
 			if (expr__parse(&result, ctx, pe->metric_expr)) {
-				expr_failure("Parse failed", map, pe);
-				ret++;
+				/*
+				 * Parsing failed, make numbers go from large to
+				 * small which can resolve divide by zero
+				 * issues.
+				 */
+				k = 1024;
+				hashmap__for_each_entry(ctx->ids, cur, bkt)
+					expr__add_id_val(ctx, strdup(cur->key), k--);
+				if (expr__parse(&result, ctx, pe->metric_expr)) {
+					expr_failure("Parse failed", map, pe);
+					ret++;
+				}
 			}
 		}
 	}
@@ -1054,10 +1064,20 @@ static int metric_parse_fake(const char *str)
 		}
 	}
 
-	if (expr__parse(&result, ctx, str))
-		pr_err("expr__parse failed\n");
-	else
-		ret = 0;
+	ret = 0;
+	if (expr__parse(&result, ctx, str)) {
+		/*
+		 * Parsing failed, make numbers go from large to small which can
+		 * resolve divide by zero issues.
+		 */
+		i = 1024;
+		hashmap__for_each_entry(ctx->ids, cur, bkt)
+			expr__add_id_val(ctx, strdup(cur->key), i--);
+		if (expr__parse(&result, ctx, str)) {
+			pr_err("expr__parse failed\n");
+			ret = -1;
+		}
+	}
 
 out:
 	expr__ctx_free(ctx);