Subject: Re: [PATCH v4] perf metricgroup: Fix uncore metric expressions

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Thu, 17 Sep 2020 17:39:53 -0300

Em Thu, Sep 17, 2020 at 01:18:07PM -0700, Ian Rogers escreveu:
> A metric like DRAM_BW_Use has on SkylakeX events uncore_imc/cas_count_read/
> and uncore_imc/case_count_write/. These events open 6 events per socket
> with pmu names of uncore_imc_[0-5]. The current metric setup code in
> find_evsel_group assumes one ID will map to 1 event to be recorded in
> metric_events. For events with multiple matches, the first event is
> recorded in metric_events (avoiding matching >1 event with the same
> name) and the evlist_used updated so that duplicate events aren't
> removed when the evlist has unused events removed.

Namhyung, please check if you still Acks this as you provided it for v3.

Thanks,

- Arnaldo
 
> Before this change:
> $ /tmp/perf/perf stat -M DRAM_BW_Use -a -- sleep 1
> 
>  Performance counter stats for 'system wide':
> 
>              41.14 MiB  uncore_imc/cas_count_read/
>      1,002,614,251 ns   duration_time
> 
>        1.002614251 seconds time elapsed
> 
> After this change:
> $ /tmp/perf/perf stat -M DRAM_BW_Use -a -- sleep 1
> 
>  Performance counter stats for 'system wide':
> 
>             157.47 MiB  uncore_imc/cas_count_read/ #     0.00 DRAM_BW_Use
>             126.97 MiB  uncore_imc/cas_count_write/
>      1,003,019,728 ns   duration_time
> 
> Erroneous duplication introduced in:
> commit 2440689d62e9 ("perf metricgroup: Remove duped metric group events").
> 
> Fixes: ded80bda8bc9 ("perf expr: Migrate expr ids table to a hashmap").
> Reported-by: Jin Yao <[email-masked]>
> Signed-off-by: Ian Rogers <[email-masked]>
> ---
>  tools/perf/util/metricgroup.c | 75 ++++++++++++++++++++++++++---------
>  1 file changed, 56 insertions(+), 19 deletions(-)
> 
> diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> index ab5030fcfed4..d948a7f910cf 100644
> --- a/tools/perf/util/metricgroup.c
> +++ b/tools/perf/util/metricgroup.c
> @@ -150,6 +150,18 @@ static void expr_ids__exit(struct expr_ids *ids)
>  		free(ids->id[i].id);
>  }
>  
> +static bool contains_event(struct evsel **metric_events, int num_events,
> +			const char *event_name)
> +{
> +	int i;
> +
> +	for (i = 0; i < num_events; i++) {
> +		if (!strcmp(metric_events[i]->name, event_name))
> +			return true;
> +	}
> +	return false;
> +}
> +
>  /**
>   * Find a group of events in perf_evlist that correpond to those from a parsed
>   * metric expression. Note, as find_evsel_group is called in the same order as
> @@ -180,7 +192,11 @@ static struct evsel *find_evsel_group(struct evlist *perf_evlist,
>  	int i = 0, matched_events = 0, events_to_match;
>  	const int idnum = (int)hashmap__size(&pctx->ids);
>  
> -	/* duration_time is grouped separately. */
> +	/*
> +	 * duration_time is always grouped separately, when events are grouped
> +	 * (ie has_constraint is false) then ignore it in the matching loop and
> +	 * add it to metric_events at the end.
> +	 */
>  	if (!has_constraint &&
>  	    hashmap__find(&pctx->ids, "duration_time", (void **)&val_ptr))
>  		events_to_match = idnum - 1;
> @@ -207,23 +223,20 @@ static struct evsel *find_evsel_group(struct evlist *perf_evlist,
>  				sizeof(struct evsel *) * idnum);
>  			current_leader = ev->leader;
>  		}
> -		if (hashmap__find(&pctx->ids, ev->name, (void **)&val_ptr)) {
> -			if (has_constraint) {
> -				/*
> -				 * Events aren't grouped, ensure the same event
> -				 * isn't matched from two groups.
> -				 */
> -				for (i = 0; i < matched_events; i++) {
> -					if (!strcmp(ev->name,
> -						    metric_events[i]->name)) {
> -						break;
> -					}
> -				}
> -				if (i != matched_events)
> -					continue;
> -			}
> +		/*
> +		 * Check for duplicate events with the same name. For example,
> +		 * uncore_imc/cas_count_read/ will turn into 6 events per socket
> +		 * on skylakex. Only the first such event is placed in
> +		 * metric_events. If events aren't grouped then this also
> +		 * ensures that the same event in different sibling groups
> +		 * aren't both added to metric_events.
> +		 */
> +		if (contains_event(metric_events, matched_events, ev->name))
> +			continue;
> +		/* Does this event belong to the parse context? */
> +		if (hashmap__find(&pctx->ids, ev->name, (void **)&val_ptr))
>  			metric_events[matched_events++] = ev;
> -		}
> +
>  		if (matched_events == events_to_match)
>  			break;
>  	}
> @@ -239,7 +252,7 @@ static struct evsel *find_evsel_group(struct evlist *perf_evlist,
>  	}
>  
>  	if (matched_events != idnum) {
> -		/* Not whole match */
> +		/* Not a whole match */
>  		return NULL;
>  	}
>  
> @@ -247,8 +260,32 @@ static struct evsel *find_evsel_group(struct evlist *perf_evlist,
>  
>  	for (i = 0; i < idnum; i++) {
>  		ev = metric_events[i];
> -		ev->metric_leader = ev;
> +		/* Don't free the used events. */
>  		set_bit(ev->idx, evlist_used);
> +		/*
> +		 * The metric leader points to the identically named event in
> +		 * metric_events.
> +		 */
> +		ev->metric_leader = ev;
> +		/*
> +		 * Mark two events with identical names in the same group (or
> +		 * globally) as being in use as uncore events may be duplicated
> +		 * for each pmu. Set the metric leader of such events to be the
> +		 * event that appears in metric_events.
> +		 */
> +		evlist__for_each_entry_continue(perf_evlist, ev) {
> +			/*
> +			 * If events are grouped then the search can terminate
> +			 * when then group is left.
> +			 */
> +			if (!has_constraint &&
> +			    ev->leader != metric_events[i]->leader)
> +				break;
> +			if (!strcmp(metric_events[i]->name, ev->name)) {
> +				set_bit(ev->idx, evlist_used);
> +				ev->metric_leader = metric_events[i];
> +			}
> +		}
>  	}
>  
>  	return metric_events[0];
> -- 
> 2.28.0.618.gf4bc123cb7-goog
> 

-- 

- Arnaldo