linux-kernel - Re: [PATCH 02/12] perf header: Add HEADER_GROUP

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Message-ID: <20121112174534.GF18978@ghostprotocols.net>
Date:	Mon, 12 Nov 2012 14:45:34 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH 02/12] perf header: Add HEADER_GROUP_DESC feature

Em Sat, Nov 10, 2012 at 01:43:24AM +0900, Namhyung Kim escreveu:
> From: Namhyung Kim <namhyung.kim@....com>
> 
> Save group relationship information so that it can be restored when
> perf report is running.
> 
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Stephane Eranian <eranian@...gle.com>
> Acked-by: Jiri Olsa <jolsa@...hat.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

<SNIP>
  
> +static int process_group_desc(struct perf_file_section *section __maybe_unused,
> +			      struct perf_header *ph, int fd,
> +			      void *data __maybe_unused)
> +{
> +	size_t ret = -1;

why initialize ret if the first thing you do with it is...

> +	u32 i, nr, nr_groups;
> +	struct perf_session *session;
> +	struct perf_evsel *evsel, *leader = NULL;
> +	struct group_desc {
> +		char *name;
> +		u32 leader_idx;
> +		u32 nr_members;
> +	} *desc;
> +
> +	ret = read(fd, &nr_groups, sizeof(nr_groups));

assign another value?

We need to use readn instead of read, and not use ret here, just do
	if (read(fd, &nr_groups, sizeof(nr_groups)) != sizeof(nr_groups))

> +	if (ret != sizeof(nr_groups))
> +		return -1;
> +
> +	if (ph->needs_swap)
> +		nr_groups = bswap_32(nr_groups);
> +
> +	ph->env.nr_groups = nr_groups;
> +	if (!nr_groups) {
> +		pr_debug("group desc not available\n");
> +		return 0;
> +	}
> +
> +	desc = calloc(nr_groups, sizeof(*desc));
> +	if (!desc)
> +		return -1;
> +
> +	for (i = 0; i < nr_groups; i++) {
> +		desc[i].name = do_read_string(fd, ph);
> +		if (!desc[i].name)
> +			goto out_free;
> +
> +		ret = read(fd, &desc[i].leader_idx, sizeof(u32));
> +		if (ret != sizeof(u32))
> +			goto out_free;

ditto

> +
> +		ret = read(fd, &desc[i].nr_members, sizeof(u32));
> +		if (ret != sizeof(u32))
> +			goto out_free;

ditto

> +
> +		if (ph->needs_swap) {
> +			desc[i].leader_idx = bswap_32(desc[i].leader_idx);
> +			desc[i].nr_members = bswap_32(desc[i].nr_members);
> +		}
> +	}
> +
> +	/*
> +	 * Rebuild group relationship based on the group_desc
> +	 */
> +	session = container_of(ph, struct perf_session, header);
> +	session->evlist->nr_groups = nr_groups;
> +
> +	i = nr = 0;
> +	list_for_each_entry(evsel, &session->evlist->entries, node) {
> +		if (evsel->idx == (int) desc[i].leader_idx) {
> +			evsel->leader = NULL;

Humm, isn't it better to set evsel->leader to evsel, that way all
members in a group have its evsel->leader pointing to the leader and for
things like the group idx we can do just:

		evsel->idx - evsel->leader->idx

avoiding the need to special case the leader, will do that.

> +			/* {anon_group} is a dummy name */
> +			if (strcmp(desc[i].name, "{anon_group}"))
> +				evsel->group_name = desc[i].name;
> +			evsel->nr_members = desc[i].nr_members;
> +
> +			BUG_ON(i >= nr_groups);
> +			BUG_ON(nr > 0);

BUG_ON here is way too extreme, we should just bail out, testing and if
the problem is found, goto out_free

> +			leader = evsel;
> +			nr = evsel->nr_members;
> +			i++;
> +		} else if (nr) {

Humm, do we really need to test against nr? Or even use nr at all?

> +			/* This is a group member */
> +			evsel->leader = leader;
> +			/* group_idx starts from 0 */
> +			evsel->group_idx = leader->nr_members - nr;
> +			nr--;
> +		}
> +	}
> +
> +	BUG_ON(i != nr_groups);
> +	BUG_ON(nr != 0);

Too extreme, goto out_free.

And just before out_free we need to set ret = 0, otherwise we will
return...

> +out_free:
> +	while ((int) --i >= 0)
> +		free(desc[i].name);
> +	free(desc);

here, whatever value was in ret, in this patch it will be, if all goes
well, sizeof(u32) :-)

> +	return ret;
> +}
> +
>  struct feature_ops {
>  	int (*write)(int fd, struct perf_header *h, struct perf_evlist *evlist);
>  	void (*print)(struct perf_header *h, int fd, FILE *fp);
> @@ -1986,6 +2137,7 @@ static const struct feature_ops feat_ops[HEADER_LAST_FEATURE] = {
>  	FEAT_OPF(HEADER_NUMA_TOPOLOGY,	numa_topology),
>  	FEAT_OPA(HEADER_BRANCH_STACK,	branch_stack),
>  	FEAT_OPP(HEADER_PMU_MAPPINGS,	pmu_mappings),
> +	FEAT_OPP(HEADER_GROUP_DESC,	group_desc),
>  };
>  
>  struct header_print_data {
> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
> index 5f1cd6884f37..e3e7fb490310 100644
> --- a/tools/perf/util/header.h
> +++ b/tools/perf/util/header.h
> @@ -29,6 +29,7 @@ enum {
>  	HEADER_NUMA_TOPOLOGY,
>  	HEADER_BRANCH_STACK,
>  	HEADER_PMU_MAPPINGS,
> +	HEADER_GROUP_DESC,
>  	HEADER_LAST_FEATURE,
>  	HEADER_FEAT_BITS	= 256,
>  };

Here we're adding holes to the struct:

> @@ -79,6 +80,7 @@ struct perf_session_env {
>  	char			*numa_nodes;
>  	int			nr_pmu_mappings;

4 byte hole

>  	char			*pmu_mappings;

4 byte hole

> +	int			nr_groups;

I'm working on a patch implementing my suggestions.

>  };
>  
>  struct perf_header {
> -- 
> 1.7.9.2
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