[PATCH] No need to protect current->group_info in sys_getgroups(), in_group_p() and...
commit231bed205879236357171e50bd8965e70797ecdc
authorEric Dumazet <dada1@resalehost.networksolutions.com>
Sat, 25 Mar 2006 11:08:00 +0000 (25 03:08 -0800)
committerLinus Torvalds <torvalds@g5.osdl.org>
Sat, 25 Mar 2006 16:22:58 +0000 (25 08:22 -0800)
treefe3bb52388510eca3fc19548abd26f4009b94db1
parent76c67de460b3d00b7ab8a96bb18f07ca47d65fba
[PATCH] No need to protect current->group_info in sys_getgroups(), in_group_p() and in_egroup_p()

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: Eric Dumazet <dada1@cosmosbay.com>
Cc: Tim Hockin <thockin@hockin.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
kernel/sys.c