linux-kernel - [PATCH v4 2/4] cpuacct: small restruct for cpuacct

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Date:	Tue, 22 Mar 2016 16:37:06 +0800
From:	Zhao Lei <zhaolei@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>, Tejun Heo <htejun@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Zhao Lei <zhaolei@...fujitsu.com>
Subject: [PATCH v4 2/4] cpuacct: small restruct for cpuacct

1: Use for() instead of while() loop in some functions
   to make code simple.
2: Use this_cpu_ptr() instead of per_cpu_ptr() to make code
   clean with little performance up.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Zhao Lei <zhaolei@...fujitsu.com>
---
 kernel/sched/cpuacct.c | 28 +++++-----------------------
 kernel/sched/cpuacct.h |  4 ++--
 2 files changed, 7 insertions(+), 25 deletions(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 9c2bbf7..434c2fa 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -238,23 +238,10 @@ static struct cftype files[] = {
 void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
 	struct cpuacct *ca;
-	int cpu;
-
-	cpu = task_cpu(tsk);
 
 	rcu_read_lock();
-
-	ca = task_ca(tsk);
-
-	while (true) {
-		u64 *cpuusage = per_cpu_ptr(ca->cpuusage, cpu);
-		*cpuusage += cputime;
-
-		ca = parent_ca(ca);
-		if (!ca)
-			break;
-	}
-
+	for (ca = task_ca(tsk); ca; ca = parent_ca(ca))
+		*this_cpu_ptr(ca->cpuusage) += cputime;
 	rcu_read_unlock();
 }
 
@@ -263,18 +250,13 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
  *
  * Note: it's the caller that updates the account of the root cgroup.
  */
-void cpuacct_account_field(struct task_struct *p, int index, u64 val)
+void cpuacct_account_field(struct task_struct *tsk, int index, u64 val)
 {
-	struct kernel_cpustat *kcpustat;
 	struct cpuacct *ca;
 
 	rcu_read_lock();
-	ca = task_ca(p);
-	while (ca != &root_cpuacct) {
-		kcpustat = this_cpu_ptr(ca->cpustat);
-		kcpustat->cpustat[index] += val;
-		ca = parent_ca(ca);
-	}
+	for (ca = task_ca(tsk); ca != &root_cpuacct; ca = parent_ca(ca))
+		this_cpu_ptr(ca->cpustat)->cpustat[index] += val;
 	rcu_read_unlock();
 }
 
diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h
index ed60562..ba72807 100644
--- a/kernel/sched/cpuacct.h
+++ b/kernel/sched/cpuacct.h
@@ -1,7 +1,7 @@
 #ifdef CONFIG_CGROUP_CPUACCT
 
 extern void cpuacct_charge(struct task_struct *tsk, u64 cputime);
-extern void cpuacct_account_field(struct task_struct *p, int index, u64 val);
+extern void cpuacct_account_field(struct task_struct *tsk, int index, u64 val);
 
 #else
 
@@ -10,7 +10,7 @@ static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 }
 
 static inline void
-cpuacct_account_field(struct task_struct *p, int index, u64 val)
+cpuacct_account_field(struct task_struct *tsk, int index, u64 val)
 {
 }
 
-- 
1.8.5.1