Commit d35b3289 authored by Wang Nan's avatar Wang Nan Committed by Arnaldo Carvalho de Melo

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.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent ad0dd7ae
......@@ -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 @@ preproc_gen_prologue(struct bpf_program *prog, int n,
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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