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>

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 72bd971..b2aaaba 100644 (file)
--- 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 bd0409b..45c1682 100644 (file)
--- 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);
 }