[PATCH] Optimize sys_times for a single thread process

Avoid taking the tasklist_lock in sys_times if the process is single
threaded.  In a NUMA system taking the tasklist_lock may cause a bouncing
cacheline if multiple independent processes continually call sys_times to
measure their performance.

Signed-off-by: Christoph Lameter <christoph@lameter.com>
Signed-off-by: Shai Fultheim <shai@scalex86.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/exit.c

@@ -72,6 +72,11 @@ repeat:
 	BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
 	__exit_signal(p);
 	__exit_sighand(p);
+	/*
+	 * Note that the fastpath in sys_times depends on __exit_signal having
+	 * updated the counters before a task is removed from the tasklist of
+	 * the process by __unhash_process.
+	 */
 	__unhash_process(p);
 
 	/*