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    Subject[RFC][PATCH 6/8] sched: scale down cpu_power due to RT tasks
    Keep an average on the amount of time spend on RT tasks and use that
    fraction to scale down the cpu_power for regular tasks.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/sched.h | 1
    kernel/sched.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++---
    kernel/sched_rt.c | 6 +---
    kernel/sysctl.c | 8 ++++++
    4 files changed, 72 insertions(+), 7 deletions(-)

    Index: linux-2.6/include/linux/sched.h
    ===================================================================
    --- linux-2.6.orig/include/linux/sched.h
    +++ linux-2.6/include/linux/sched.h
    @@ -1863,6 +1863,7 @@ extern unsigned int sysctl_sched_child_r
    extern unsigned int sysctl_sched_features;
    extern unsigned int sysctl_sched_migration_cost;
    extern unsigned int sysctl_sched_nr_migrate;
    +extern unsigned int sysctl_sched_time_avg;
    extern unsigned int sysctl_timer_migration;

    int sched_nr_latency_handler(struct ctl_table *table, int write,
    Index: linux-2.6/kernel/sched.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched.c
    +++ linux-2.6/kernel/sched.c
    @@ -627,6 +627,9 @@ struct rq {

    struct task_struct *migration_thread;
    struct list_head migration_queue;
    +
    + u64 rt_avg;
    + u64 age_stamp;
    #endif

    /* calc_load related fields */
    @@ -863,6 +866,14 @@ unsigned int sysctl_sched_shares_ratelim
    unsigned int sysctl_sched_shares_thresh = 4;

    /*
    + * period over which we average the RT time consumption, measured
    + * in ms.
    + *
    + * default: 1s
    + */
    +const_debug unsigned int sysctl_sched_time_avg = MSEC_PER_SEC;
    +
    +/*
    * period over which we measure -rt task cpu usage in us.
    * default: 1s
    */
    @@ -1280,12 +1291,37 @@ void wake_up_idle_cpu(int cpu)
    }
    #endif /* CONFIG_NO_HZ */

    +static u64 sched_avg_period(void)
    +{
    + return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;
    +}
    +
    +static void sched_avg_update(struct rq *rq)
    +{
    + s64 period = sched_avg_period();
    +
    + while ((s64)(rq->clock - rq->age_stamp) > period) {
    + rq->age_stamp += period;
    + rq->rt_avg /= 2;
    + }
    +}
    +
    +static void sched_rt_avg_update(struct rq *rq, u64 rt_delta)
    +{
    + rq->rt_avg += rt_delta;
    + sched_avg_update(rq);
    +}
    +
    #else /* !CONFIG_SMP */
    static void resched_task(struct task_struct *p)
    {
    assert_spin_locked(&task_rq(p)->lock);
    set_tsk_need_resched(p);
    }
    +
    +static void sched_rt_avg_update(struct rq *rq, u64 rt_delta)
    +{
    +}
    #endif /* CONFIG_SMP */

    #if BITS_PER_LONG == 32
    @@ -3699,7 +3735,7 @@ static inline int check_power_save_busie
    }
    #endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */

    -unsigned long __weak arch_smt_gain(struct sched_domain *sd, int cpu)
    +unsigned long __weak arch_scale_smt_power(struct sched_domain *sd, int cpu)
    {
    unsigned long weight = cpumask_weight(sched_domain_span(sd));
    unsigned long smt_gain = sd->smt_gain;
    @@ -3709,6 +3745,24 @@ unsigned long __weak arch_smt_gain(struc
    return smt_gain;
    }

    +unsigned long scale_rt_power(int cpu)
    +{
    + struct rq *rq = cpu_rq(cpu);
    + u64 total, available;
    +
    + sched_avg_update(rq);
    +
    + total = sched_avg_period() + (rq->clock - rq->age_stamp);
    + available = total - rq->rt_avg;
    +
    + if (unlikely((s64)total < SCHED_LOAD_SCALE))
    + total = SCHED_LOAD_SCALE;
    +
    + total >>= SCHED_LOAD_SHIFT;
    +
    + return div_u64(available, total);
    +}
    +
    static void update_cpu_power(struct sched_domain *sd, int cpu)
    {
    unsigned long weight = cpumask_weight(sched_domain_span(sd));
    @@ -3719,11 +3773,15 @@ static void update_cpu_power(struct sche
    /* here we could scale based on cpufreq */

    if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
    - power *= arch_smt_gain(sd, cpu);
    + power *= arch_scale_smt_power(sd, cpu);
    power >>= SCHED_LOAD_SHIFT;
    }

    - /* here we could scale based on RT time */
    + power *= scale_rt_power(cpu);
    + power >>= SCHED_LOAD_SHIFT;
    +
    + if (!power)
    + power = 1;

    if (power != old) {
    sdg->__cpu_power = power;
    Index: linux-2.6/kernel/sched_rt.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched_rt.c
    +++ linux-2.6/kernel/sched_rt.c
    @@ -615,6 +615,8 @@ static void update_curr_rt(struct rq *rq
    curr->se.exec_start = rq->clock;
    cpuacct_charge(curr, delta_exec);

    + sched_rt_avg_update(rq, delta_exec);
    +
    if (!rt_bandwidth_enabled())
    return;

    @@ -887,8 +889,6 @@ static void enqueue_task_rt(struct rq *r

    if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
    enqueue_pushable_task(rq, p);
    -
    - inc_cpu_load(rq, p->se.load.weight);
    }

    static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
    @@ -899,8 +899,6 @@ static void dequeue_task_rt(struct rq *r
    dequeue_rt_entity(rt_se);

    dequeue_pushable_task(rq, p);
    -
    - dec_cpu_load(rq, p->se.load.weight);
    }

    /*
    Index: linux-2.6/kernel/sysctl.c
    ===================================================================
    --- linux-2.6.orig/kernel/sysctl.c
    +++ linux-2.6/kernel/sysctl.c
    @@ -332,6 +332,14 @@ static struct ctl_table kern_table[] = {
    },
    {
    .ctl_name = CTL_UNNUMBERED,
    + .procname = "sched_time_avg",
    + .data = &sysctl_sched_time_avg,
    + .maxlen = sizeof(unsigned int),
    + .mode = 0644,
    + .proc_handler = &proc_dointvec,
    + },
    + {
    + .ctl_name = CTL_UNNUMBERED,
    .procname = "timer_migration",
    .data = &sysctl_timer_migration,
    .maxlen = sizeof(unsigned int),
    --



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