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Subject[tip:sched/core] sched/accounting: Re-use scheduler statistics for the root cgroup
Commit-ID:  54c707e98de9ca899e6552a47c797c62c45885ee
Gitweb: http://git.kernel.org/tip/54c707e98de9ca899e6552a47c797c62c45885ee
Author: Glauber Costa <glommer@parallels.com>
AuthorDate: Mon, 28 Nov 2011 14:45:19 -0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 6 Dec 2011 20:51:21 +0100

sched/accounting: Re-use scheduler statistics for the root cgroup

Right now, after we collect tick statistics for user and system and store them
in a well known location, we keep the same statistics again for cpuacct.
Since cpuacct is hierarchical, the numbers for the root cgroup should be
absolutely equal to the system-wide numbers.

So it would be better to just use it: this patch changes cpuacct accounting
in a way that the cpustat statistics are kept in a struct kernel_cpustat percpu
array. In the root cgroup case, we just point it to the main array. The rest of
the hierarchy walk can be totally disabled later with a static branch - but I am
not doing it here.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Tuner <pjt@google.com>
Link: http://lkml.kernel.org/r/1322498719-2255-4-git-send-email-glommer@parallels.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched/core.c | 165 +++++++++++++++++++++++---------------------------
kernel/sched/sched.h | 34 +++++++++-
2 files changed, 106 insertions(+), 93 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a727c4e..3e078f2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2556,6 +2556,42 @@ unsigned long long task_sched_runtime(struct task_struct *p)
return ns;
}

+#ifdef CONFIG_CGROUP_CPUACCT
+struct cgroup_subsys cpuacct_subsys;
+struct cpuacct root_cpuacct;
+#endif
+
+static inline void task_group_account_field(struct task_struct *p,
+ u64 tmp, int index)
+{
+#ifdef CONFIG_CGROUP_CPUACCT
+ struct kernel_cpustat *kcpustat;
+ struct cpuacct *ca;
+#endif
+ /*
+ * Since all updates are sure to touch the root cgroup, we
+ * get ourselves ahead and touch it first. If the root cgroup
+ * is the only cgroup, then nothing else should be necessary.
+ *
+ */
+ __get_cpu_var(kernel_cpustat).cpustat[index] += tmp;
+
+#ifdef CONFIG_CGROUP_CPUACCT
+ if (unlikely(!cpuacct_subsys.active))
+ return;
+
+ rcu_read_lock();
+ ca = task_ca(p);
+ while (ca && (ca != &root_cpuacct)) {
+ kcpustat = this_cpu_ptr(ca->cpustat);
+ kcpustat->cpustat[index] += tmp;
+ ca = parent_ca(ca);
+ }
+ rcu_read_unlock();
+#endif
+}
+
+
/*
* Account user cpu time to a process.
* @p: the process that the cpu time gets accounted to
@@ -2580,7 +2616,7 @@ void account_user_time(struct task_struct *p, cputime_t cputime,
index = (TASK_NICE(p) > 0) ? CPUTIME_NICE : CPUTIME_USER;
cpustat[index] += tmp;

- cpuacct_update_stats(p, CPUACCT_STAT_USER, cputime);
+ task_group_account_field(p, index, cputime);
/* Account for user time used */
acct_update_integrals(p);
}
@@ -2636,7 +2672,7 @@ void __account_system_time(struct task_struct *p, cputime_t cputime,

/* Add system time to cpustat. */
cpustat[index] += tmp;
- cpuacct_update_stats(p, CPUACCT_STAT_SYSTEM, cputime);
+ task_group_account_field(p, index, cputime);

/* Account for system time used */
acct_update_integrals(p);
@@ -6781,8 +6817,15 @@ void __init sched_init(void)
INIT_LIST_HEAD(&root_task_group.children);
INIT_LIST_HEAD(&root_task_group.siblings);
autogroup_init(&init_task);
+
#endif /* CONFIG_CGROUP_SCHED */

+#ifdef CONFIG_CGROUP_CPUACCT
+ root_cpuacct.cpustat = &kernel_cpustat;
+ root_cpuacct.cpuusage = alloc_percpu(u64);
+ /* Too early, not expected to fail */
+ BUG_ON(!root_cpuacct.cpuusage);
+#endif
for_each_possible_cpu(i) {
struct rq *rq;

@@ -7843,44 +7886,16 @@ struct cgroup_subsys cpu_cgroup_subsys = {
* (balbir@in.ibm.com).
*/

-/* track cpu usage of a group of tasks and its child groups */
-struct cpuacct {
- struct cgroup_subsys_state css;
- /* cpuusage holds pointer to a u64-type object on every cpu */
- u64 __percpu *cpuusage;
- struct percpu_counter cpustat[CPUACCT_STAT_NSTATS];
-};
-
-struct cgroup_subsys cpuacct_subsys;
-
-/* return cpu accounting group corresponding to this container */
-static inline struct cpuacct *cgroup_ca(struct cgroup *cgrp)
-{
- return container_of(cgroup_subsys_state(cgrp, cpuacct_subsys_id),
- struct cpuacct, css);
-}
-
-/* return cpu accounting group to which this task belongs */
-static inline struct cpuacct *task_ca(struct task_struct *tsk)
-{
- return container_of(task_subsys_state(tsk, cpuacct_subsys_id),
- struct cpuacct, css);
-}
-
-static inline struct cpuacct *parent_ca(struct cpuacct *ca)
-{
- if (!ca || !ca->css.cgroup->parent)
- return NULL;
- return cgroup_ca(ca->css.cgroup->parent);
-}
-
/* create a new cpu accounting group */
static struct cgroup_subsys_state *cpuacct_create(
struct cgroup_subsys *ss, struct cgroup *cgrp)
{
- struct cpuacct *ca = kzalloc(sizeof(*ca), GFP_KERNEL);
- int i;
+ struct cpuacct *ca;

+ if (!cgrp->parent)
+ return &root_cpuacct.css;
+
+ ca = kzalloc(sizeof(*ca), GFP_KERNEL);
if (!ca)
goto out;

@@ -7888,15 +7903,13 @@ static struct cgroup_subsys_state *cpuacct_create(
if (!ca->cpuusage)
goto out_free_ca;

- for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
- if (percpu_counter_init(&ca->cpustat[i], 0))
- goto out_free_counters;
+ ca->cpustat = alloc_percpu(struct kernel_cpustat);
+ if (!ca->cpustat)
+ goto out_free_cpuusage;

return &ca->css;

-out_free_counters:
- while (--i >= 0)
- percpu_counter_destroy(&ca->cpustat[i]);
+out_free_cpuusage:
free_percpu(ca->cpuusage);
out_free_ca:
kfree(ca);
@@ -7909,10 +7922,8 @@ static void
cpuacct_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
{
struct cpuacct *ca = cgroup_ca(cgrp);
- int i;

- for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
- percpu_counter_destroy(&ca->cpustat[i]);
+ free_percpu(ca->cpustat);
free_percpu(ca->cpuusage);
kfree(ca);
}
@@ -8005,16 +8016,31 @@ static const char *cpuacct_stat_desc[] = {
};

static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft,
- struct cgroup_map_cb *cb)
+ struct cgroup_map_cb *cb)
{
struct cpuacct *ca = cgroup_ca(cgrp);
- int i;
+ int cpu;
+ s64 val = 0;

- for (i = 0; i < CPUACCT_STAT_NSTATS; i++) {
- s64 val = percpu_counter_read(&ca->cpustat[i]);
- val = cputime64_to_clock_t(val);
- cb->fill(cb, cpuacct_stat_desc[i], val);
+ for_each_online_cpu(cpu) {
+ struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
+ val += kcpustat->cpustat[CPUTIME_USER];
+ val += kcpustat->cpustat[CPUTIME_NICE];
}
+ val = cputime64_to_clock_t(val);
+ cb->fill(cb, cpuacct_stat_desc[CPUACCT_STAT_USER], val);
+
+ val = 0;
+ for_each_online_cpu(cpu) {
+ struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
+ val += kcpustat->cpustat[CPUTIME_SYSTEM];
+ val += kcpustat->cpustat[CPUTIME_IRQ];
+ val += kcpustat->cpustat[CPUTIME_SOFTIRQ];
+ }
+
+ val = cputime64_to_clock_t(val);
+ cb->fill(cb, cpuacct_stat_desc[CPUACCT_STAT_SYSTEM], val);
+
return 0;
}

@@ -8066,45 +8092,6 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
rcu_read_unlock();
}

-/*
- * When CONFIG_VIRT_CPU_ACCOUNTING is enabled one jiffy can be very large
- * in cputime_t units. As a result, cpuacct_update_stats calls
- * percpu_counter_add with values large enough to always overflow the
- * per cpu batch limit causing bad SMP scalability.
- *
- * To fix this we scale percpu_counter_batch by cputime_one_jiffy so we
- * batch the same amount of time with CONFIG_VIRT_CPU_ACCOUNTING disabled
- * and enabled. We cap it at INT_MAX which is the largest allowed batch value.
- */
-#ifdef CONFIG_SMP
-#define CPUACCT_BATCH \
- min_t(long, percpu_counter_batch * cputime_one_jiffy, INT_MAX)
-#else
-#define CPUACCT_BATCH 0
-#endif
-
-/*
- * Charge the system/user time to the task's accounting group.
- */
-void cpuacct_update_stats(struct task_struct *tsk,
- enum cpuacct_stat_index idx, cputime_t val)
-{
- struct cpuacct *ca;
- int batch = CPUACCT_BATCH;
-
- if (unlikely(!cpuacct_subsys.active))
- return;
-
- rcu_read_lock();
- ca = task_ca(tsk);
-
- do {
- __percpu_counter_add(&ca->cpustat[idx], val, batch);
- ca = parent_ca(ca);
- } while (ca);
- rcu_read_unlock();
-}
-
struct cgroup_subsys cpuacct_subsys = {
.name = "cpuacct",
.create = cpuacct_create,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d88545c..c248016 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -830,13 +830,39 @@ extern void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime
extern void update_cpu_load(struct rq *this_rq);

#ifdef CONFIG_CGROUP_CPUACCT
+#include <linux/cgroup.h>
+/* track cpu usage of a group of tasks and its child groups */
+struct cpuacct {
+ struct cgroup_subsys_state css;
+ /* cpuusage holds pointer to a u64-type object on every cpu */
+ u64 __percpu *cpuusage;
+ struct kernel_cpustat __percpu *cpustat;
+};
+
+/* return cpu accounting group corresponding to this container */
+static inline struct cpuacct *cgroup_ca(struct cgroup *cgrp)
+{
+ return container_of(cgroup_subsys_state(cgrp, cpuacct_subsys_id),
+ struct cpuacct, css);
+}
+
+/* return cpu accounting group to which this task belongs */
+static inline struct cpuacct *task_ca(struct task_struct *tsk)
+{
+ return container_of(task_subsys_state(tsk, cpuacct_subsys_id),
+ struct cpuacct, css);
+}
+
+static inline struct cpuacct *parent_ca(struct cpuacct *ca)
+{
+ if (!ca || !ca->css.cgroup->parent)
+ return NULL;
+ return cgroup_ca(ca->css.cgroup->parent);
+}
+
extern void cpuacct_charge(struct task_struct *tsk, u64 cputime);
-extern void cpuacct_update_stats(struct task_struct *tsk,
- enum cpuacct_stat_index idx, cputime_t val);
#else
static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime) {}
-static inline void cpuacct_update_stats(struct task_struct *tsk,
- enum cpuacct_stat_index idx, cputime_t val) {}
#endif

static inline void inc_nr_running(struct rq *rq)

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