[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>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index c2bdf6fb61a5..3ebcd60a19c6 100644
--- a/kernel/exit.c
+++ b/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);
 
         /*