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perf bpf: Collect perf_evsel in BPF object files 

This patch creates a 'struct perf_evsel' for every probe in a BPF object
file(s) and fills 'struct evlist' with them. The previously introduced
dummy event is now removed. After this patch, the following command:

 # perf record --event filter.o ls

Can trace on each of the probes defined in filter.o.

The core of this patch is bpf__foreach_tev(), which calls a callback
function for each 'struct probe_trace_event' event for a bpf program
with each associated file descriptors. The add_bpf_event() callback
creates evsels by calling parse_events_add_tracepoint().

Since bpf-loader.c will not be built if libbpf is turned off, an empty
bpf__foreach_tev() is defined in bpf-loader.h to avoid build errors.

Committer notes:

Before:

  # /tmp/oldperf record --event /tmp/foo.o -a usleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.198 MB perf.data ]
  # perf evlist
  /tmp/foo.o
  # perf evlist -v
  /tmp/foo.o: type: 1, size: 112, config: 0x9, { sample_period,
  sample_freq }: 4000, sample_type: IP|TID|TIME|CPU|PERIOD, disabled: 1,
  inherit: 1, mmap: 1, comm: 1, freq: 1, task: 1, sample_id_all: 1,
  exclude_guest: 1, mmap2: 1, comm_exec: 1

I.e. we create just the PERF_TYPE_SOFTWARE (type: 1),
PERF_COUNT_SW_DUMMY(config 0x9) event, now, with this patch:

  # perf record --event /tmp/foo.o -a usleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.210 MB perf.data ]
  # perf evlist -v
  perf_bpf_probe:fork: type: 2, size: 112, config: 0x6bd, { sample_period,
  sample_freq }: 1, sample_type: IP|TID|TIME|CPU|PERIOD|RAW, disabled: 1,
  inherit: 1, mmap: 1, comm: 1, task: 1, sample_id_all: 1, exclude_guest:
  1, mmap2: 1, comm_exec: 1
  #

We now have a PERF_TYPE_SOFTWARE (type: 1), but the config states 0x6bd,
which is how, after setting up the event via the kprobes interface, the
'perf_bpf_probe:fork' event is accessible via the perf_event_open
syscall. This is all transient, as soon as the 'perf record' session
ends, these probes will go away.

To see how it looks like, lets try doing a neverending session, one that
expects a control+C to end:

  # perf record --event /tmp/foo.o -a

So, with that in place, we can use 'perf probe' to see what is in place:

  # perf probe -l
    perf_bpf_probe:fork  (on _do_fork@acme/git/linux/kernel/fork.c)

We also can use debugfs:

  [root@felicio ~]# cat /sys/kernel/debug/tracing/kprobe_events
  p:perf_bpf_probe/fork _text+638512

Ok, now lets stop and see if we got some forks:

  [root@felicio linux]# perf record --event /tmp/foo.o -a
  ^C[ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.325 MB perf.data (111 samples) ]

  [root@felicio linux]# perf script
      sshd  1271 [003] 81797.507678: perf_bpf_probe:fork: (ffffffff8109be30)
      sshd 18309 [000] 81797.524917: perf_bpf_probe:fork: (ffffffff8109be30)
      sshd 18309 [001] 81799.381603: perf_bpf_probe:fork: (ffffffff8109be30)
      sshd 18309 [001] 81799.408635: perf_bpf_probe:fork: (ffffffff8109be30)
  <SNIP>

Sure enough, we have 111 forks :-)

Callchains seems to work as well:

  # perf report --stdio --no-child
  # To display the perf.data header info, please use --header/--header-only options.
  #
  # Total Lost Samples: 0
  #
  # Samples: 562  of event 'perf_bpf_probe:fork'
  # Event count (approx.): 562
  #
  # Overhead  Command   Shared Object     Symbol
  # ........  ........  ................  ............
  #
      44.66%  sh        [kernel.vmlinux]  [k] _do_fork
                    |
                    ---_do_fork
                       entry_SYSCALL_64_fastpath
                       __libc_fork
                       make_child

    26.16%  make      [kernel.vmlinux]  [k] _do_fork
<SNIP>
  #

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1444826502-49291-7-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Wang Nan 2015-10-14 12:41:17 +00:00 committed by Arnaldo Carvalho de Melo
parent 1e5e3ee8ff
commit 4edf30e39e
3 changed files with 99 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
tools/perf/util/bpf-loader.c
View File

@ -255,6 +255,46 @@ int bpf__load(struct bpf_object *obj)
return 0;
}
int bpf__foreach_tev(struct bpf_object *obj,
bpf_prog_iter_callback_t func,
void *arg)
{
struct bpf_program *prog;
int err;
bpf_object__for_each_program(prog, obj) {
struct probe_trace_event *tev;
struct perf_probe_event *pev;
struct bpf_prog_priv *priv;
int i, fd;
err = bpf_program__get_private(prog,
(void **)&priv);
if (err || !priv) {
pr_debug("bpf: failed to get private field\n");
return -EINVAL;
}
pev = &priv->pev;
for (i = 0; i < pev->ntevs; i++) {
tev = &pev->tevs[i];
fd = bpf_program__fd(prog);
if (fd < 0) {
pr_debug("bpf: failed to get file descriptor\n");
return fd;
}
err = (*func)(tev, fd, arg);
if (err) {
pr_debug("bpf: call back failed, stop iterate\n");
return err;
}
}
}
return 0;
}
#define bpf__strerror_head(err, buf, size) \
char sbuf[STRERR_BUFSIZE], *emsg;\
if (!size)\

14
tools/perf/util/bpf-loader.h
View File

@ -8,11 +8,15 @@
#include <linux/compiler.h>
#include <linux/err.h>
#include <string.h>
#include "probe-event.h"
#include "debug.h"
struct bpf_object;
#define PERF_BPF_PROBE_GROUP "perf_bpf_probe"
typedef int (*bpf_prog_iter_callback_t)(struct probe_trace_event *tev,
int fd, void *arg);
#ifdef HAVE_LIBBPF_SUPPORT
struct bpf_object *bpf__prepare_load(const char *filename);
@ -26,6 +30,8 @@ int bpf__strerror_probe(struct bpf_object *obj, int err,
int bpf__load(struct bpf_object *obj);
int bpf__strerror_load(struct bpf_object *obj, int err,
char *buf, size_t size);
int bpf__foreach_tev(struct bpf_object *obj,
bpf_prog_iter_callback_t func, void *arg);
#else
static inline struct bpf_object *
bpf__prepare_load(const char *filename __maybe_unused)
@ -40,6 +46,14 @@ static inline int bpf__probe(struct bpf_object *obj __maybe_unused) { return 0;}
static inline int bpf__unprobe(struct bpf_object *obj __maybe_unused) { return 0;}
static inline int bpf__load(struct bpf_object *obj __maybe_unused) { return 0; }
static inline int
bpf__foreach_tev(struct bpf_object *obj __maybe_unused,
bpf_prog_iter_callback_t func __maybe_unused,
void *arg __maybe_unused)
{
return 0;
}
static inline int
__bpf_strerror(char *buf, size_t size)
{

52
tools/perf/util/parse-events.c
View File

@ -530,12 +530,49 @@ static int add_tracepoint_multi_sys(struct list_head *list, int *idx,
return ret;
}
struct __add_bpf_event_param {
struct parse_events_evlist *data;
struct list_head *list;
};
static int add_bpf_event(struct probe_trace_event *tev, int fd,
void *_param)
{
LIST_HEAD(new_evsels);
struct __add_bpf_event_param *param = _param;
struct parse_events_evlist *evlist = param->data;
struct list_head *list = param->list;
int err;
pr_debug("add bpf event %s:%s and attach bpf program %d\n",
tev->group, tev->event, fd);
err = parse_events_add_tracepoint(&new_evsels, &evlist->idx, tev->group,
tev->event, evlist->error, NULL);
if (err) {
struct perf_evsel *evsel, *tmp;
pr_debug("Failed to add BPF event %s:%s\n",
tev->group, tev->event);
list_for_each_entry_safe(evsel, tmp, &new_evsels, node) {
list_del(&evsel->node);
perf_evsel__delete(evsel);
}
return err;
}
pr_debug("adding %s:%s\n", tev->group, tev->event);
list_splice(&new_evsels, list);
return 0;
}
int parse_events_load_bpf_obj(struct parse_events_evlist *data,
struct list_head *list,
struct bpf_object *obj)
{
int err;
char errbuf[BUFSIZ];
struct __add_bpf_event_param param = {data, list};
static bool registered_unprobe_atexit = false;
if (IS_ERR(obj) || !obj) {
@ -567,13 +604,14 @@ int parse_events_load_bpf_obj(struct parse_events_evlist *data,
goto errout;
}
/*
* Temporary add a dummy event here so we can check whether
* basic bpf loader works. Following patches will replace
* dummy event by useful evsels.
*/
return parse_events_add_numeric(data, list, PERF_TYPE_SOFTWARE,
PERF_COUNT_SW_DUMMY, NULL);
err = bpf__foreach_tev(obj, add_bpf_event, &param);
if (err) {
snprintf(errbuf, sizeof(errbuf),
"Attach events in BPF object failed");
goto errout;
}
return 0;
errout:
data->error->help = strdup("(add -v to see detail)");
data->error->str = strdup(errbuf);