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[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>
This commit is contained in:
Eric Dumazet 2006-03-25 03:08:00 -08:00 committed by Linus Torvalds
parent 76c67de460
commit 231bed2058
1 changed files with 0 additions and 6 deletions
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6
kernel/sys.c
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@ -1421,7 +1421,6 @@ asmlinkage long sys_getgroups(int gidsetsize, gid_t __user *grouplist)
return -EINVAL;
/* no need to grab task_lock here; it cannot change */
get_group_info(current->group_info);
i = current->group_info->ngroups;
if (gidsetsize) {
if (i > gidsetsize) {
@ -1434,7 +1433,6 @@ asmlinkage long sys_getgroups(int gidsetsize, gid_t __user *grouplist)
}
}
out:
put_group_info(current->group_info);
return i;
}
@ -1475,9 +1473,7 @@ int in_group_p(gid_t grp)
{
int retval = 1;
if (grp != current->fsgid) {
get_group_info(current->group_info);
retval = groups_search(current->group_info, grp);
put_group_info(current->group_info);
}
return retval;
}
@ -1488,9 +1484,7 @@ int in_egroup_p(gid_t grp)
{
int retval = 1;
if (grp != current->egid) {
get_group_info(current->group_info);
retval = groups_search(current->group_info, grp);
put_group_info(current->group_info);
}
return retval;
}