linux-kernel - [PATCH v2] perf test: Make metric testing more robust.

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Date:   Wed, 22 Sep 2021 10:24:27 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     eranian@...gle.com, Ian Rogers <irogers@...gle.com>
Subject: [PATCH v2] 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)

v2. Rebase and more detail in commit message.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/tests/pmu-events.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/tools/perf/tests/pmu-events.c b/tools/perf/tests/pmu-events.c
index 43743cf719ef..0ed11764cfab 100644
--- a/tools/perf/tests/pmu-events.c
+++ b/tools/perf/tests/pmu-events.c
@@ -891,8 +891,18 @@ static int test_parsing(void)
 			}
 
 			if (expr__parse(&result, &ctx, pe->metric_expr, 0)) {
-				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, 0)) {
+					expr_failure("Parse failed", map, pe);
+					ret++;
+				}
 			}
 			expr__ctx_clear(&ctx);
 		}
@@ -947,10 +957,20 @@ static int metric_parse_fake(const char *str)
 		}
 	}
 
-	if (expr__parse(&result, &ctx, str, 0))
-		pr_err("expr__parse failed\n");
-	else
-		ret = 0;
+	ret = 0;
+	if (expr__parse(&result, &ctx, str, 0)) {
+		/*
+		 * 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, 0)) {
+			pr_err("expr__parse failed\n");
+			ret = -1;
+		}
+	}
 
 out:
 	expr__ctx_clear(&ctx);
-- 
2.33.0.464.g1972c5931b-goog