Commit d35b3289 authored by Wang Nan's avatar Wang Nan Committed by Arnaldo Carvalho de Melo
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perf bpf: Use same BPF program if arguments are identical 



This patch allows creating only one BPF program for different
'probe_trace_event'(tev) entries generated by one
'perf_probe_event'(pev) if their prologues are identical.

This is done by comparing the argument list of different tev instances,
and the maps type of prologue and tev using a mapping array. This patch
utilizes qsort to sort the tevs. After sorting, tevs with identical
argument lists will be grouped together.

Test result:

Sample BPF program:

  #define SEC(NAME) __attribute__((section(NAME), used))
  SEC("inlines=no;"
      "func=SyS_dup? oldfd")
  int func(void *ctx)
  {
      return 1;
  }

It would probe at SyS_dup2 and SyS_dup3, obtaining oldfd as its
argument.

The following cmdline shows a BPF program being loaded into the kernel
by perf:

 # perf record -e ./test_bpf_arg.c sleep 4 & sleep 1 && ls /proc/$!/fd/ -l | grep bpf-prog

Before this patch:

  # perf record -e ./test_bpf_arg.c sleep 4 & sleep 1 && ls /proc/$!/fd/ -l | grep bpf-prog
  [1] 24858
  lrwx------ 1 root root 64 Nov 14 04:09 3 -> anon_inode:bpf-prog
  lrwx------ 1 root root 64 Nov 14 04:09 4 -> anon_inode:bpf-prog
  ...

After this patch:

  # perf record -e ./test_bpf_arg.c sleep 4 & sleep 1 && ls /proc/$!/fd/ -l | grep bpf-prog
  [1] 25699
  lrwx------ 1 root root 64 Nov 14 04:10 3 -> anon_inode:bpf-prog
  ...

Signed-off-by: default avatarWang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1447749170-175898-3-git-send-email-wangnan0@huawei.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent ad0dd7ae

tools/perf/util/bpf-loader.c

+131 −7
Original line number Diff line number Diff line
@@ -38,6 +38,8 @@ struct bpf_prog_priv { 
	struct perf_probe_event pev;

	bool need_prologue;

	struct bpf_insn *insns_buf;

	int nr_types;

	int *type_mapping;

};



static bool libbpf_initialized;
@@ -113,6 +115,7 @@ bpf_prog_priv__clear(struct bpf_program *prog __maybe_unused, 


	cleanup_perf_probe_events(&priv->pev, 1);

	zfree(&priv->insns_buf);

	zfree(&priv->type_mapping);

	free(priv);

}
@@ -381,7 +384,7 @@ preproc_gen_prologue(struct bpf_program *prog, int n, 
	struct bpf_prog_priv *priv;

	struct bpf_insn *buf;

	size_t prologue_cnt = 0;

	int err;

	int i, err;



	err = bpf_program__get_private(prog, (void **)&priv);

	if (err || !priv)
@@ -389,10 +392,21 @@ preproc_gen_prologue(struct bpf_program *prog, int n, 


	pev = &priv->pev;



	if (n < 0 || n >= pev->ntevs)

	if (n < 0 || n >= priv->nr_types)

		goto errout;



	tev = &pev->tevs[n];

	/* Find a tev belongs to that type */

	for (i = 0; i < pev->ntevs; i++) {

		if (priv->type_mapping[i] == n)

			break;

	}



	if (i >= pev->ntevs) {

		pr_debug("Internal error: prologue type %d not found\n", n);

		return -BPF_LOADER_ERRNO__PROLOGUE;

	}



	tev = &pev->tevs[i];



	buf = priv->insns_buf;

	err = bpf__gen_prologue(tev->args, tev->nargs,
@@ -423,6 +437,101 @@ errout: 
	return -BPF_LOADER_ERRNO__PROLOGUE;

}



/*

 * compare_tev_args is reflexive, transitive and antisymmetric.

 * I can proof it but this margin is too narrow to contain.

 */

static int compare_tev_args(const void *ptev1, const void *ptev2)

{

	int i, ret;

	const struct probe_trace_event *tev1 =

		*(const struct probe_trace_event **)ptev1;

	const struct probe_trace_event *tev2 =

		*(const struct probe_trace_event **)ptev2;



	ret = tev2->nargs - tev1->nargs;

	if (ret)

		return ret;



	for (i = 0; i < tev1->nargs; i++) {

		struct probe_trace_arg *arg1, *arg2;

		struct probe_trace_arg_ref *ref1, *ref2;



		arg1 = &tev1->args[i];

		arg2 = &tev2->args[i];



		ret = strcmp(arg1->value, arg2->value);

		if (ret)

			return ret;



		ref1 = arg1->ref;

		ref2 = arg2->ref;



		while (ref1 && ref2) {

			ret = ref2->offset - ref1->offset;

			if (ret)

				return ret;



			ref1 = ref1->next;

			ref2 = ref2->next;

		}



		if (ref1 || ref2)

			return ref2 ? 1 : -1;

	}



	return 0;

}



/*

 * Assign a type number to each tevs in a pev.

 * mapping is an array with same slots as tevs in that pev.

 * nr_types will be set to number of types.

 */

static int map_prologue(struct perf_probe_event *pev, int *mapping,

			int *nr_types)

{

	int i, type = 0;

	struct probe_trace_event **ptevs;



	size_t array_sz = sizeof(*ptevs) * pev->ntevs;



	ptevs = malloc(array_sz);

	if (!ptevs) {

		pr_debug("No ehough memory: alloc ptevs failed\n");

		return -ENOMEM;

	}



	pr_debug("In map_prologue, ntevs=%d\n", pev->ntevs);

	for (i = 0; i < pev->ntevs; i++)

		ptevs[i] = &pev->tevs[i];



	qsort(ptevs, pev->ntevs, sizeof(*ptevs),

	      compare_tev_args);



	for (i = 0; i < pev->ntevs; i++) {

		int n;



		n = ptevs[i] - pev->tevs;

		if (i == 0) {

			mapping[n] = type;

			pr_debug("mapping[%d]=%d\n", n, type);

			continue;

		}



		if (compare_tev_args(ptevs + i, ptevs + i - 1) == 0)

			mapping[n] = type;

		else

			mapping[n] = ++type;



		pr_debug("mapping[%d]=%d\n", n, mapping[n]);

	}

	free(ptevs);

	*nr_types = type + 1;



	return 0;

}



static int hook_load_preprocessor(struct bpf_program *prog)

{

	struct perf_probe_event *pev;
@@ -462,7 +571,19 @@ static int hook_load_preprocessor(struct bpf_program *prog) 
		return -ENOMEM;

	}



	err = bpf_program__set_prep(prog, pev->ntevs,

	priv->type_mapping = malloc(sizeof(int) * pev->ntevs);

	if (!priv->type_mapping) {

		pr_debug("No enough memory: alloc type_mapping failed\n");

		return -ENOMEM;

	}

	memset(priv->type_mapping, -1,

	       sizeof(int) * pev->ntevs);



	err = map_prologue(pev, priv->type_mapping, &priv->nr_types);

	if (err)

		return err;



	err = bpf_program__set_prep(prog, priv->nr_types,

				    preproc_gen_prologue);

	return err;

}
@@ -596,10 +717,13 @@ int bpf__foreach_tev(struct bpf_object *obj, 
		for (i = 0; i < pev->ntevs; i++) {

			tev = &pev->tevs[i];



			if (priv->need_prologue)

				fd = bpf_program__nth_fd(prog, i);

			else

			if (priv->need_prologue) {

				int type = priv->type_mapping[i];



				fd = bpf_program__nth_fd(prog, type);

			} else {

				fd = bpf_program__fd(prog);

			}



			if (fd < 0) {

				pr_debug("bpf: failed to get file descriptor\n");

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