• Eric Dumazet's avatar
    [PATCH] No need to protect current->group_info in sys_getgroups(), in_group_p() and in_egroup_p() · 231bed20
    Eric Dumazet authored
    
    
    While doing some benchmarks of an Apache/PHP SMP server, I noticed high
    oprofile numbers in in_group_p() and _atomic_dec_and_lock().
    
    rank  percent
      1     4.8911 % __link_path_walk
      2     4.8503 % __d_lookup
    *3     4.2911 % _atomic_dec_and_lock
      4     3.9307 % __copy_to_user_ll
      5     4.9004 % sysenter_past_esp
    *6     3.3248 % in_group_p
    
    It appears that in_group_p() does an uncessary
    
    get_group_info(current->group_info); /* atomic_inc() */
      ... /* access current->group_info */
    put_group_info(current->group_info); /* _atomic_dec_and_lock */
    
    It is not necessary to do this, because the current task holds a reference
    on its own group_info, and this reference cannot change during the lookup.
    
    This patch deletes the get_group_info()/put_group_info() pair from
    sys_getgroups(), in_group_p() and in_egroup_p() functions.
    Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Cc: Tim Hockin <thockin@hockin.org>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    231bed20