sched: Introduce task_times() to replace task_{u,s}time() pair

Functions task_{u,s}time() are called in pair in almost all
cases.  However task_stime() is implemented to call task_utime()
from its inside, so such paired calls run task_utime() twice.

It means we do heavy divisions (div_u64 + do_div) twice to get
utime and stime which can be obtained at same time by one set
of divisions.

This patch introduces a function task_times(*tsk, *utime,
*stime) to retrieve utime and stime at once in better, optimized
way.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Spencer Candland <spencer@bluehost.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Americo Wang <xiyou.wangcong@gmail.com>
LKML-Reference: <4B0E16AE.906@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1 insertions, 2 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index ce17760d9c51..bbdfce0d4347 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1346,8 +1346,7 @@ static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
         utime = stime = cputime_zero;
 
         if (who == RUSAGE_THREAD) {
-                utime = task_utime(current);
-                stime = task_stime(current);
+                task_times(current, &utime, &stime);
                 accumulate_thread_rusage(p, r);
                 maxrss = p->signal->maxrss;
                 goto out;