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

[John Garry]

On 04/08/2021 08:25, 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. 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)

is this the standard method to make the metric evaluation fail when 
results are not as expected? In this example, event2 should be greater 
than event3 always. Dividing by max(x, 0) would seem a bit silly.

thanks,
John

> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>   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 b8aff8fb50d8..6c1cd58605c1 100644
> --- a/tools/perf/tests/pmu-events.c
> +++ b/tools/perf/tests/pmu-events.c
> @@ -600,8 +600,18 @@ 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);
>   		}
> @@ -656,10 +666,20 @@ 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);