[tip:sched/urgent] sched/cpuacct: Simplify the cpuacct code

[tip-bot for Zhao Lei <tipbot@zytor.com>]

Commit-ID:  73e6aafd9ea81498d31361f01db84a0118da2d1c
Gitweb:     http://git.kernel.org/tip/73e6aafd9ea81498d31361f01db84a0118da2d1c
Author:     Zhao Lei <zhaolei@cn.fujitsu.com>
AuthorDate: Thu, 17 Mar 2016 12:19:43 +0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 21 Mar 2016 11:00:28 +0100

sched/cpuacct: Simplify the cpuacct code

 - Use for() instead of while() loop in some functions
   to make the code simpler.

 - Use this_cpu_ptr() instead of per_cpu_ptr() to make the code
   cleaner and a bit faster.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/d8a7ef9592f55224630cb26dea239f05b6398a4e.1458187654.git.zhaolei@cn.fujitsu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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)
 {
 }