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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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