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Subject[PATCH v2 10/14] Keep number of context switches per-cgroup
Date
This patch ties the number of context_switches to a cgroup.
No impact is expected when per-cgroup stats collecting is disabled
in the root cgroup.

Signed-off-by: Glauber Costa <glommer@parallels.com>
---
include/linux/kernel_stat.h | 2 ++
kernel/sched.c | 24 ++++++++++++++++++------
kernel/sched_debug.c | 3 ++-
3 files changed, 22 insertions(+), 7 deletions(-)
diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 77e91f6..2c32b24 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -30,6 +30,7 @@ enum cpu_usage_stat {
STEAL_BASE,
IDLE_BASE,
TOTAL_FORKS,
+ NR_SWITCHES,
NR_STATS,
};

@@ -68,6 +69,7 @@ DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat);


extern unsigned long long nr_context_switches(void);
+extern unsigned long long nr_context_switches_cpu(int cpu);

#ifndef CONFIG_GENERIC_HARDIRQS

diff --git a/kernel/sched.c b/kernel/sched.c
index 800728e..4f91781 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -611,7 +611,6 @@ struct rq {
/* capture load from *all* tasks on this cpu: */
struct load_weight load;
unsigned long nr_load_updates;
- u64 nr_switches;

struct cfs_rq cfs;
struct rt_rq rt;
@@ -3475,11 +3474,23 @@ unsigned long long nr_context_switches(void)
int i;
unsigned long long sum = 0;

- for_each_possible_cpu(i)
- sum += cpu_rq(i)->nr_switches;
+ for_each_possible_cpu(i) {
+ kstat_lock();
+ sum += per_cpu(kernel_cpustat, i).cpustat[NR_SWITCHES];
+ kstat_unlock();
+ }

return sum;
}
+unsigned long long nr_context_switches_cpu(int cpu)
+{
+ unsigned long long ret;
+
+ kstat_lock();
+ ret = per_cpu(kernel_cpustat, cpu).cpustat[NR_SWITCHES];
+ kstat_unlock();
+ return ret;
+}

unsigned long nr_iowait(void)
{
@@ -4554,9 +4565,9 @@ need_resched:
rq->skip_clock_update = 0;

if (likely(prev != next)) {
- rq->nr_switches++;
rq->curr = next;
++*switch_count;
+ task_group_account_field(prev, 1, NR_SWITCHES);

context_switch(rq, prev, next); /* unlocks the rq */
/*
@@ -9713,6 +9724,7 @@ int cpu_cgroup_proc_stat(struct cgroup *cgrp, struct cftype *cft,
unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
struct timespec boottime;
unsigned long tg_iowait = 0;
+ u64 tg_nr_switches = 0;
#ifdef CONFIG_CGROUP_SCHED
struct task_group *tg;
struct task_group *sib;
@@ -9754,8 +9766,8 @@ int cpu_cgroup_proc_stat(struct cgroup *cgrp, struct cftype *cft,
guest += kcpustat->cpustat[GUEST];
guest_nice += kcpustat->cpustat[GUEST_NICE];
total_forks += kcpustat->cpustat[TOTAL_FORKS];
+ tg_nr_switches += kcpustat->cpustat[NR_SWITCHES];
tg_iowait += atomic_read(&kcpustat->nr_iowait);
-
#ifdef CONFIG_CGROUP_SCHED
if (static_branch(&sched_cgroup_enabled)) {
list_for_each_entry(sib, &tg->siblings, siblings) {
@@ -9858,7 +9870,7 @@ int cpu_cgroup_proc_stat(struct cgroup *cgrp, struct cftype *cft,
"processes %llu\n"
"procs_running %lu\n"
"procs_blocked %lu\n",
- nr_context_switches(),
+ tg_nr_switches,
(unsigned long)jif,
total_forks,
nr_running(),
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index a6710a1..c7464601 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -246,6 +246,7 @@ static void print_cpu(struct seq_file *m, int cpu)
{
struct rq *rq = cpu_rq(cpu);
unsigned long flags;
+ unsigned long long nr_switches = nr_context_switches_cpu(cpu);

#ifdef CONFIG_X86
{
@@ -266,8 +267,8 @@ static void print_cpu(struct seq_file *m, int cpu)
P(nr_running);
SEQ_printf(m, " .%-30s: %lu\n", "load",
rq->load.weight);
- P(nr_switches);
P(nr_load_updates);
+ SEQ_printf(m, " .%-30s: %Ld\n","nr_switches", nr_switches);
P(nr_uninterruptible);
PN(next_balance);
P(curr->pid);
--
1.7.6.4


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