[PATCH 0/5] cpuacct, cgroup: Remove cgroup_subsys.active

[PATCH 0/5] cpuacct, cgroup: Remove cgroup_subsys.active

[Li Zefan]

cpuacct is the only user of cgroup_subsys.active flag.

The flag is needed because cpuacct_charge() and cpuacct_account_field() can
be called when cpuacct hasn't been initialized during system bootup.

This patch initializes cpuacct earlier, and the result is we don't have
to check the flag in scheduler hot path.

Note, this patchset is based on "[PATCH 0/7] sched: Split cpuacct"
(just because there're code conflicts)

	http://lkml.org/lkml/2013/3/28/1

0001-cpuacct-allocate-per_cpu-cpuusage-for-root-cpuacct-s.patch
0002-cpuacct-Initialize-root-cpuacct-earlier.patch
0003-cpuacct-Initialize-cpuacct-subsystem-earlier.patch
0004-cpuacct-No-need-to-check-subsys-active-state.patch
0005-cgroup-Remove-subsys.active-flag.patch

--
 include/linux/cgroup.h |  1 -
 kernel/cgroup.c        |  3 ---
 kernel/sched/core.c    |  2 --
 kernel/sched/cpuacct.c | 30 +++++++++++-------------------
 kernel/sched/cpuacct.h |  5 -----
 5 files changed, 11 insertions(+), 30 deletions(-)

[PATCH 1/5] cpuacct: Allocate per_cpu cpuusage for root cpuacct statically

[Li Zefan]

This is a preparation, so later we can initialize cpuacct earlier.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 kernel/sched/cpuacct.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 9305fd2..a691c4d 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -58,6 +58,7 @@ static inline struct cpuacct *parent_ca(struct cpuacct *ca)
 	return cgroup_ca(ca->css.cgroup->parent);
 }
 
+static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
 static struct cpuacct root_cpuacct;
 
 /* create a new cpu accounting group */
@@ -290,8 +291,7 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
 void __init cpuacct_init(void)
 {
 	root_cpuacct.cpustat = &kernel_cpustat;
-	root_cpuacct.cpuusage = alloc_percpu(u64);
-	BUG_ON(!root_cpuacct.cpuusage); /* Too early, not expected to fail */
+	root_cpuacct.cpuusage = &root_cpuacct_cpuusage;
 }
 
 struct cgroup_subsys cpuacct_subsys = {
-- 
1.8.0.2

[PATCH 2/5] cpuacct: Initialize root cpuacct earlier

[Li Zefan]

Now we don't need cpuacct_init(), and instead we just initialize
root_cpuacct when it's defined.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 kernel/sched/core.c    |  2 --
 kernel/sched/cpuacct.c | 11 ++++-------
 kernel/sched/cpuacct.h |  5 -----
 3 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9f5a804..e12649c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6860,8 +6860,6 @@ void __init sched_init(void)
 
 #endif /* CONFIG_CGROUP_SCHED */
 
-	cpuacct_init();
-
 	for_each_possible_cpu(i) {
 		struct rq *rq;
 
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index a691c4d..0425581 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -59,7 +59,10 @@ static inline struct cpuacct *parent_ca(struct cpuacct *ca)
 }
 
 static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
-static struct cpuacct root_cpuacct;
+static struct cpuacct root_cpuacct = {
+	.cpustat	= &kernel_cpustat,
+	.cpuusage	= &root_cpuacct_cpuusage,
+};
 
 /* create a new cpu accounting group */
 static struct cgroup_subsys_state *cpuacct_css_alloc(struct cgroup *cgrp)
@@ -288,12 +291,6 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
 	rcu_read_unlock();
 }
 
-void __init cpuacct_init(void)
-{
-	root_cpuacct.cpustat = &kernel_cpustat;
-	root_cpuacct.cpuusage = &root_cpuacct_cpuusage;
-}
-
 struct cgroup_subsys cpuacct_subsys = {
 	.name = "cpuacct",
 	.css_alloc = cpuacct_css_alloc,
diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h
index 51cd76e..ed60562 100644
--- a/kernel/sched/cpuacct.h
+++ b/kernel/sched/cpuacct.h
@@ -1,15 +1,10 @@
 #ifdef CONFIG_CGROUP_CPUACCT
 
-extern void cpuacct_init(void);
 extern void cpuacct_charge(struct task_struct *tsk, u64 cputime);
 extern void cpuacct_account_field(struct task_struct *p, int index, u64 val);
 
 #else
 
-static inline void cpuacct_init(void)
-{
-}
-
 static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
 }
-- 
1.8.0.2

[PATCH 3/5] cpuacct: Initialize cpuacct subsystem earlier

[Li Zefan]

Initialize cpuacct before the scheduler is functioning, so when
cpuacct_charge() and cpuacct_account_field() are called, task_ca()
won't return NULL.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 kernel/sched/cpuacct.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 0425581..75e46d2 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -292,9 +292,10 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
 }
 
 struct cgroup_subsys cpuacct_subsys = {
-	.name = "cpuacct",
-	.css_alloc = cpuacct_css_alloc,
-	.css_free = cpuacct_css_free,
-	.subsys_id = cpuacct_subsys_id,
-	.base_cftypes = files,
+	.name		= "cpuacct",
+	.css_alloc	= cpuacct_css_alloc,
+	.css_free	= cpuacct_css_free,
+	.subsys_id	= cpuacct_subsys_id,
+	.base_cftypes	= files,
+	.early_init	= 1,
 };
-- 
1.8.0.2

[PATCH 4/5] cpuacct: No need to check subsys active state

[Li Zefan]

Now we're guaranteed when cpuacct_charge() and cpuacct_account_field()
are called, cpuacct has already been properly initialized, so we no
longer need those checks.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 kernel/sched/cpuacct.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 75e46d2..ef57ab6 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -247,9 +247,6 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 	struct cpuacct *ca;
 	int cpu;
 
-	if (unlikely(!cpuacct_subsys.active))
-		return;
-
 	cpu = task_cpu(tsk);
 
 	rcu_read_lock();
@@ -278,9 +275,6 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
 	struct kernel_cpustat *kcpustat;
 	struct cpuacct *ca;
 
-	if (unlikely(!cpuacct_subsys.active))
-		return;
-
 	rcu_read_lock();
 	ca = task_ca(p);
 	while (ca != &root_cpuacct) {
-- 
1.8.0.2

[PATCH 5/5] cgroup: Remove subsys.active flag

[Li Zefan]

The only user was cpuacct.

Signed-off-by: Li Zefan <lizefan@huawei.com>
---
 include/linux/cgroup.h | 1 -
 kernel/cgroup.c        | 3 ---
 2 files changed, 4 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7d73905..a236a5b 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -457,7 +457,6 @@ struct cgroup_subsys {
 	void (*bind)(struct cgroup *root);
 
 	int subsys_id;
-	int active;
 	int disabled;
 	int early_init;
 	/*
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4855892..64dd57d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4415,7 +4415,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 	 * need to invoke fork callbacks here. */
 	BUG_ON(!list_empty(&init_task.tasks));
 
-	ss->active = 1;
 	BUG_ON(online_css(ss, dummytop));
 
 	mutex_unlock(&cgroup_mutex);
@@ -4523,7 +4522,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
 	}
 	write_unlock(&css_set_lock);
 
-	ss->active = 1;
 	ret = online_css(ss, dummytop);
 	if (ret)
 		goto err_unload;
@@ -4565,7 +4563,6 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
 	mutex_lock(&cgroup_mutex);
 
 	offline_css(ss, dummytop);
-	ss->active = 0;
 
 	if (ss->use_id) {
 		idr_remove_all(&ss->idr);
-- 
1.8.0.2

Re: [PATCH 5/5] cgroup: Remove subsys.active flag

[Tejun Heo]

On Thu, Mar 28, 2013 at 03:21:49PM +0800, Li Zefan wrote:
> The only user was cpuacct.
> 
> Signed-off-by: Li Zefan <lizefan@huawei.com>

  Acked-by: Tejun Heo <tj@kernel.org>

Please feel free to route through -tip with the other cpuacct changes.

Thanks.

-- 
tejun