netdev - Re: [PATCH v2 perf,bpf 08/11] perf, bpf: save btf information as headers to perf.data

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Date:   Fri, 15 Feb 2019 17:25:01 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <acme@...hat.com>
CC:     Jiri Olsa <jolsa@...nel.org>, Netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "acme@...nel.org" <acme@...nel.org>
Subject: Re: [PATCH v2 perf,bpf 08/11] perf, bpf: save btf information as
 headers to perf.data



> On Feb 15, 2019, at 6:26 AM, Arnaldo Carvalho de Melo <acme@...hat.com> wrote:
> 
> Em Thu, Feb 14, 2019 at 04:00:09PM -0800, Song Liu escreveu:
>> This patch enables perf-record to save btf information as headers to
>> perf.data A new header type HEADER_BTF is introduced for this data.
> 
> Jiri,
> 
> 	Wouldn't it be better for this HEADER_BTF to be introduced
> already as an user space event, Song, see:
> 
>  tools/perf/util/event.h
> 
> and:
> 
>  tools/perf/util/event.c
> 
> perf_event__synthesize_cpu_map()
> 
> - Arnaldo
> 

BTF would be short living for short living BPF programs. I guess 
saving them as header is easier than merging them with samples. 

What's the benefit of saving them as user space events?

Thanks,
Song


> 
>> Signed-off-by: Song Liu <songliubraving@...com>
>> ---
>> tools/perf/util/header.c | 99 +++++++++++++++++++++++++++++++++++++++-
>> tools/perf/util/header.h |  1 +
>> 2 files changed, 99 insertions(+), 1 deletion(-)
>> 
>> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
>> index 2ae76a9d06f6..3f1562afe8e5 100644
>> --- a/tools/perf/util/header.c
>> +++ b/tools/perf/util/header.c
>> @@ -1125,6 +1125,45 @@ static int write_bpf_prog_info(struct feat_fd *ff,
>> 	return ret;
>> }
>> 
>> +static int write_btf(struct feat_fd *ff,
>> +		     struct perf_evlist *evlist __maybe_unused)
>> +{
>> +	struct perf_env *env = &ff->ph->env;
>> +	struct rb_root *root;
>> +	struct rb_node *next;
>> +	u32 count = 0;
>> +	int ret;
>> +
>> +	down_read(&env->bpf_info_lock);
>> +
>> +	root = &env->btfs;
>> +	next = rb_first(root);
>> +	while (next) {
>> +		++count;
>> +		next = rb_next(next);
>> +	}
>> +
>> +	ret = do_write(ff, &count, sizeof(count));
>> +
>> +	if (ret < 0)
>> +		goto out;
>> +
>> +	next = rb_first(root);
>> +	while (next) {
>> +		struct btf_node *node;
>> +
>> +		node = rb_entry(next, struct btf_node, rb_node);
>> +		next = rb_next(&node->rb_node);
>> +		ret = do_write(ff, node,
>> +			       sizeof(struct btf_node) + node->data_size);
>> +		if (ret < 0)
>> +			goto out;
>> +	}
>> +out:
>> +	up_read(&env->bpf_info_lock);
>> +	return ret;
>> +}
>> +
>> static int cpu_cache_level__sort(const void *a, const void *b)
>> {
>> 	struct cpu_cache_level *cache_a = (struct cpu_cache_level *)a;
>> @@ -1628,6 +1667,28 @@ static void print_bpf_prog_info(struct feat_fd *ff, FILE *fp)
>> 	up_read(&env->bpf_info_lock);
>> }
>> 
>> +static void print_btf(struct feat_fd *ff, FILE *fp)
>> +{
>> +	struct perf_env *env = &ff->ph->env;
>> +	struct rb_root *root;
>> +	struct rb_node *next;
>> +
>> +	down_read(&env->bpf_info_lock);
>> +
>> +	root = &env->btfs;
>> +	next = rb_first(root);
>> +
>> +	while (next) {
>> +		struct btf_node *node;
>> +
>> +		node = rb_entry(next, struct btf_node, rb_node);
>> +		next = rb_next(&node->rb_node);
>> +		fprintf(fp, "# bpf_prog_info of id %u\n", node->id);
>> +	}
>> +
>> +	up_read(&env->bpf_info_lock);
>> +}
>> +
>> static void free_event_desc(struct perf_evsel *events)
>> {
>> 	struct perf_evsel *evsel;
>> @@ -2723,6 +2784,41 @@ static int process_bpf_prog_info(struct feat_fd *ff,
>> 	return err;
>> }
>> 
>> +static int process_btf(struct feat_fd *ff, void *data __maybe_unused)
>> +{
>> +	struct perf_env *env = &ff->ph->env;
>> +	u32 count, i;
>> +
>> +	if (do_read_u32(ff, &count))
>> +		return -1;
>> +
>> +	down_write(&env->bpf_info_lock);
>> +
>> +	for (i = 0; i < count; ++i) {
>> +		struct btf_node btf_node;
>> +		struct btf_node *node;
>> +
>> +		if (__do_read(ff, &btf_node, sizeof(struct btf_node)))
>> +			return -1;
>> +
>> +		node = malloc(sizeof(struct btf_node) + btf_node.data_size);
>> +		if (!node)
>> +			return -1;
>> +
>> +		node->id = btf_node.id;
>> +		node->data_size = btf_node.data_size;
>> +
>> +		if (__do_read(ff, node->data, btf_node.data_size)) {
>> +			free(node);
>> +			return -1;
>> +		}
>> +		perf_env__insert_btf(env, node);
>> +	}
>> +
>> +	up_write(&env->bpf_info_lock);
>> +	return 0;
>> +}
>> +
>> struct feature_ops {
>> 	int (*write)(struct feat_fd *ff, struct perf_evlist *evlist);
>> 	void (*print)(struct feat_fd *ff, FILE *fp);
>> @@ -2783,7 +2879,8 @@ static const struct feature_ops feat_ops[HEADER_LAST_FEATURE] = {
>> 	FEAT_OPR(SAMPLE_TIME,	sample_time,	false),
>> 	FEAT_OPR(MEM_TOPOLOGY,	mem_topology,	true),
>> 	FEAT_OPR(CLOCKID,       clockid,        false),
>> -	FEAT_OPR(BPF_PROG_INFO, bpf_prog_info,  false)
>> +	FEAT_OPR(BPF_PROG_INFO, bpf_prog_info,  false),
>> +	FEAT_OPR(BTF,           btf,            false)
>> };
>> 
>> struct header_print_data {
>> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
>> index 0785c91b4c3a..ba51d8e43c53 100644
>> --- a/tools/perf/util/header.h
>> +++ b/tools/perf/util/header.h
>> @@ -40,6 +40,7 @@ enum {
>> 	HEADER_MEM_TOPOLOGY,
>> 	HEADER_CLOCKID,
>> 	HEADER_BPF_PROG_INFO,
>> +	HEADER_BTF,
>> 	HEADER_LAST_FEATURE,
>> 	HEADER_FEAT_BITS	= 256,
>> };
>> -- 
>> 2.17.1