linux-kernel - Re: [V3 PATCH] perf parse-events: Specially handle uncore event alias in small groups

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Message-ID: <20180426161410.GC2122@krava>
Date:   Thu, 26 Apr 2018 18:14:10 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, namhyung@...nel.org,
        ganapatrao.kulkarni@...ium.com, zhangshaokun@...ilicon.com,
        yao.jin@...ux.intel.com, will.deacon@....com, ak@...ux.intel.com,
        agustinv@...eaurora.org
Subject: Re: [V3 PATCH] perf parse-events: Specially handle uncore event
 alias in small groups

On Wed, Apr 25, 2018 at 10:58:43AM -0700, kan.liang@...ux.intel.com wrote:

SNIP

> -void parse_events__set_leader(char *name, struct list_head *list)
> +/*
> + * Check if the two uncore PMUs are from the same uncore block
> + * The format of the uncore PMU name is uncore_#blockname_#pmuidx
> + */
> +static bool is_same_uncore_block(const char *pmu_name_a, const char *pmu_name_b)
> +{
> +	char *end_a, *end_b;
> +
> +	end_a = strrchr(pmu_name_a, '_');
> +	end_b = strrchr(pmu_name_b, '_');
> +
> +	if (!end_a || !end_b)
> +		return false;
> +
> +	if ((end_a - pmu_name_a) != (end_b - pmu_name_b))
> +		return false;
> +
> +	return (strncmp(pmu_name_a, pmu_name_b, end_a - pmu_name_a) == 0);
> +}
> +
> +static int
> +parse_events__set_leader_for_uncore_aliase(char *name, struct list_head *list,
> +					   struct parse_events_state *parse_state)
> +{
> +	struct perf_evsel *evsel, *leader;
> +	uintptr_t *leaders;
> +	bool is_leader = true;
> +	int i = 0, nr_pmu = 0, total_members, ret = 0;
> +
> +	leader = list_entry(list->next, struct perf_evsel, node);
> +	evsel = list_entry(list->prev, struct perf_evsel, node);

could you please use list_last_entry and list_first_entry in here?

> +	total_members = evsel->idx - leader->idx + 1;
> +
> +	leaders = calloc(total_members, sizeof(uintptr_t));
> +	if (!leaders)
> +		return ret;

returns 0 in here

> +
> +	 __evlist__for_each_entry(list, evsel) {
> +
> +		/* Only split the uncore group which members use alias */
> +		if (!evsel->use_uncore_alias)
> +			goto out;
> +
> +		/* The events must be from the same uncore block */
> +		if (!is_same_uncore_block(leader->pmu_name, evsel->pmu_name))
> +			goto out;
> +
> +		if (!is_leader)
> +			continue;
> +		/*
> +		 * If the event's PMU name starts to repeat, it must be a new
> +		 * event. That can be used to distinguish the leader from
> +		 * other members, even they have the same event name.
> +		 */
> +		if ((leader != evsel) && (leader->pmu_name == evsel->pmu_name)) {
> +			is_leader = false;

setting "is_leader = false" basically breaks the loop,
because of that !leader check above, so why continue?

> +			continue;
> +		}
> +		/* The name is always alias name */
> +		WARN_ON(strcmp(leader->name, evsel->name));
> +
> +		leaders[nr_pmu++] = (uintptr_t) evsel;
> +	}
> +
> +	/* only one event alias */
> +	if (nr_pmu == total_members) {
> +		parse_state->nr_groups--;
> +		goto handled;
> +	}
> +
> +	__evlist__for_each_entry(list, evsel) {
> +		if (i >= nr_pmu)
> +			i = 0;
> +		evsel->leader = (struct perf_evsel *) leaders[i++];
> +	}

it's not so obvious from the code how the groups
are set.. please describe that logic in the comment

thanks,
jirka

> +
> +	for (i = 0; i < nr_pmu; i++) {
> +		evsel = (struct perf_evsel *) leaders[i];
> +		evsel->nr_members = total_members / nr_pmu;
> +		evsel->group_name = name ? strdup(name) : NULL;
> +	}
> +
> +	parse_state->nr_groups += nr_pmu - 1;
> +
> +handled:
> +	ret = 1;
> +out:
> +	free(leaders);
> +	return ret;
> +}