sched/cpuacct: Remove redundant NULL checks in cpuacct_charge()

This is a micro optimization for the hot path.

- We don't need to check if @ca is NULL in parent_ca().
- We don't need to check if @ca is NULL in the beginning of the for loop.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/515536A9.5000700@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 6 insertions, 2 deletions

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 72bd971ea377..b2aaaba16d46 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -210,9 +210,13 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 
         ca = task_ca(tsk);
 
-        for (; ca; ca = parent_ca(ca)) {
+        while (true) {
                 u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
                 *cpuusage += cputime;
+
+                ca = parent_ca(ca);
+                if (!ca)
+                        break;
         }
 
         rcu_read_unlock();
diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h
index bd0409b85525..45c168207fcc 100644
--- a/kernel/sched/cpuacct.h
+++ b/kernel/sched/cpuacct.h
@@ -36,7 +36,7 @@ static inline struct cpuacct *task_ca(struct task_struct *tsk)
 
 static inline struct cpuacct *parent_ca(struct cpuacct *ca)
 {
-        if (!ca || !ca->css.cgroup->parent)
+        if (!ca->css.cgroup->parent)
                 return NULL;
         return cgroup_ca(ca->css.cgroup->parent);
 }