perf test: Make metric testing more robust.

[PATCH v3] perf test: Make metric testing more robust.

Posted by Ian Rogers 4 years, 6 months ago

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.
v3. Is a rebase.

Signed-off-by: Ian Rogers <irogers@google.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 df1c9a3cc05b..b2ddf928d32a 100644
--- a/tools/perf/tests/pmu-events.c
+++ b/tools/perf/tests/pmu-events.c
@@ -962,8 +962,18 @@ 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++;
+				}
 			}
 		}
 	}
@@ -1022,10 +1032,20 @@ 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);
-- 
2.34.1.307.g9b7440fafd-goog

Re: [PATCH v3] perf test: Make metric testing more robust.

Posted by John Garry 4 years, 6 months ago

On 23/12/2021 18:56, Ian Rogers wrote:
> 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.
> v3. Is a rebase.

Incorrect location for this info

> 
> Signed-off-by: Ian Rogers <irogers@google.com>

Reviewed-by: John Garry <john.garry@huawei.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 df1c9a3cc05b..b2ddf928d32a 100644
> --- a/tools/perf/tests/pmu-events.c
> +++ b/tools/perf/tests/pmu-events.c
> @@ -962,8 +962,18 @@ 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

can or may?

> +				 * 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++;
> +				}
>   			}
>   		}
>   	}
> @@ -1022,10 +1032,20 @@ 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);
>