• Alexei Starovoitov's avatar
    bpf: add lookup/update support for per-cpu hash and array maps · 15a07b33
    Alexei Starovoitov authored
    The functions bpf_map_lookup_elem(map, key, value) and
    bpf_map_update_elem(map, key, value, flags) need to get/set
    values from all-cpus for per-cpu hash and array maps,
    so that user space can aggregate/update them as necessary.
    
    Example of single counter aggregation in user space:
      unsigned int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
      long values[nr_cpus];
      long value = 0;
    
      bpf_lookup_elem(fd, key, values);
      for (i = 0; i < nr_cpus; i++)
        value += values[i];
    
    The user space must provide round_up(value_size, 8) * nr_cpus
    array to get/set values, since kernel will use 'long' copy
    of per-cpu values to try to copy good counters atomically.
    It's a best-effort, since bpf programs and user space are racing
    to access the same memory.
    Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    15a07b33
arraymap.c 12.3 KB