• Song Liu's avatar
    bpf: Sharing bpf runtime stats with BPF_ENABLE_STATS · d46edd67
    Song Liu authored
    Currently, sysctl kernel.bpf_stats_enabled controls BPF runtime stats.
    Typical userspace tools use kernel.bpf_stats_enabled as follows:
    
      1. Enable kernel.bpf_stats_enabled;
      2. Check program run_time_ns;
      3. Sleep for the monitoring period;
      4. Check program run_time_ns again, calculate the difference;
      5. Disable kernel.bpf_stats_enabled.
    
    The problem with this approach is that only one userspace tool can toggle
    this sysctl. If multiple tools toggle the sysctl at the same time, the
    measurement may be inaccurate.
    
    To fix this problem while keep backward compatibility, introduce a new
    bpf command BPF_ENABLE_STATS. On success, this command enables stats and
    returns a valid fd. BPF_ENABLE_STATS takes argument "type". Currently,
    only one type, BPF_STATS_RUN_TIME, is supported. We can extend the
    command to support other types of stats in the future.
    
    With BPF_ENABLE_STATS, user space tool would have the following flow:
    
      1. Get a fd with BPF_ENABLE_STATS, and make sure it is valid;
      2. Check program run_time_ns;
      3. Sleep for the monitoring period;
      4. Check program run_time_ns again, calculate the difference;
      5. Close the fd.
    Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
    Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
    Link: https://lore.kernel.org/bpf/20200430071506.1408910-2-songliubraving@fb.com
    d46edd67
sysctl.c 78.3 KB