[PATCH -tip] cpuacct: reduce one NULL check in fast-path

[Li Zefan <lizf@cn.fujitsu.com>]

In cpuacct_charge(), task_ca() will never return NULL, so change
for(...) to do{}while(...) to save one NULL check.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---

rebased on tip tree

---
 kernel/sched.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index d40964b..c167f38 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -9867,10 +9867,11 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 	cpu = task_cpu(tsk);
 	ca = task_ca(tsk);
 
-	for (; ca; ca = ca->parent) {
+	do {
 		u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
 		*cpuusage += cputime;
-	}
+		ca = ca->parent;
+	} while (ca);
 }
 
 struct cgroup_subsys cpuacct_subsys = {
-- 
1.5.4.rc3