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Date:   Tue, 15 Feb 2022 12:10:37 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     John Garry <john.garry@huawei.com>
Cc:     Ian Rogers <irogers@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Kajol Jain <kjain@linux.ibm.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        eranian@google.com
Subject: Re: [PATCH v3] perf test: Make metric testing more robust.
Message-ID: <YgvCbTBzVjBBP9/y@kernel.org>
References: <20211223185622.3435128-1-irogers@google.com>
 <e078ac0f-6165-9670-926f-d1f2c536ea9e@huawei.com>
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Em Fri, Dec 24, 2021 at 08:49:35AM +0000, John Garry escreveu:
> 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>

Found thru the cracks, applying.

- Arnaldo
 
> > ---
> >   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);
> > 

-- 

- Arnaldo