linux-kernel - [PATCH v2 6/7] cpuacct: Remove redundant NULL checks in cpuacct_acount

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Date:	Fri, 29 Mar 2013 14:37:43 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 6/7] cpuacct: Remove redundant NULL checks in cpuacct_acount_field()

This is a micro optimazation for a hot path.

- We don't need to check if @ca returned from task_ca() is NULL.
- We don't need to check if @ca returned from parent_ca() is NULL.

Signed-off-by: Li Zefan <lizefan@...wei.com>
---
 kernel/sched/cpuacct.c | 4 ++--
 kernel/sched/cpuacct.h | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index b2aaaba..071ae8d 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -237,10 +237,10 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
 
 	rcu_read_lock();
 	ca = task_ca(p);
-	while (ca && (ca != &root_cpuacct)) {
+	while (ca != &root_cpuacct) {
 		kcpustat = this_cpu_ptr(ca->cpustat);
 		kcpustat->cpustat[index] += val;
-		ca = parent_ca(ca);
+		ca = __parent_ca(ca);
 	}
 	rcu_read_unlock();
 }
diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h
index 45c1682..b2f79ad 100644
--- a/kernel/sched/cpuacct.h
+++ b/kernel/sched/cpuacct.h
@@ -34,6 +34,11 @@ static inline struct cpuacct *task_ca(struct task_struct *tsk)
 			    struct cpuacct, css);
 }
 
+static inline struct cpuacct *__parent_ca(struct cpuacct *ca)
+{
+	return cgroup_ca(ca->css.cgroup->parent);
+}
+
 static inline struct cpuacct *parent_ca(struct cpuacct *ca)
 {
 	if (!ca->css.cgroup->parent)
-- 
1.8.0.2
--
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