• Wang Nan's avatar
    perf bpf: Collect perf_evsel in BPF object files · 4edf30e3
    Wang Nan authored
    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: default avatarWang Nan <wangnan0@huawei.com>
    Tested-by: default avatarArnaldo 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.comSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    4edf30e3
bpf-loader.c 7.03 KB