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Date: Thu, 25 Feb 2010 13:44:38 +0530
From: Bharata B Rao <bharata@...ux.vnet.ibm.com>
To: Paul <pjt@...gle.com>
Cc: linux-kernel@...r.kernel.org, Paul Menage <menage@...gle.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Gautham R Shenoy <ego@...ibm.com>,
Dhaval Giani <dhaval.giani@...il.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Herbert Poetzl <herbert@...hfloor.at>,
Chris Friesen <cfriesen@...tel.com>,
Avi Kivity <avi@...hat.com>, Nikhil Rao <ncrao@...gle.com>,
Ingo Molnar <mingo@...e.hu>,
Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
Mike Waychison <mikew@...gle.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC PATCH v1 1/4] sched: introduce primitives to account for
CFS bandwidth tracking
On Fri, Feb 12, 2010 at 06:54:57PM -0800, Paul wrote:
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -190,10 +190,28 @@ static inline int rt_bandwidth_enabled(void)
> return sysctl_sched_rt_runtime >= 0;
> }
>
> -static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
> +static void start_bandwidth_timer(struct hrtimer *period_timer, ktime_t period)
> {
> - ktime_t now;
> + unsigned long delta;
> + ktime_t soft, hard, now;
> +
> + for (;;) {
> + if (hrtimer_active(period_timer))
> + break;
> +
> + now = hrtimer_cb_get_time(period_timer);
> + hrtimer_forward(period_timer, now, period);
> +
> + soft = hrtimer_get_softexpires(period_timer);
> + hard = hrtimer_get_expires(period_timer);
> + delta = ktime_to_ns(ktime_sub(hard, soft));
> + __hrtimer_start_range_ns(period_timer, soft, delta,
> + HRTIMER_MODE_ABS_PINNED, 0);
> + }
> +}
>
> +static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
> +{
> if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
> return;
>
> @@ -201,22 +219,7 @@ static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
> return;
>
> raw_spin_lock(&rt_b->rt_runtime_lock);
> - for (;;) {
> - unsigned long delta;
> - ktime_t soft, hard;
> -
> - if (hrtimer_active(&rt_b->rt_period_timer))
> - break;
> -
> - now = hrtimer_cb_get_time(&rt_b->rt_period_timer);
> - hrtimer_forward(&rt_b->rt_period_timer, now, rt_b->rt_period);
> -
> - soft = hrtimer_get_softexpires(&rt_b->rt_period_timer);
> - hard = hrtimer_get_expires(&rt_b->rt_period_timer);
> - delta = ktime_to_ns(ktime_sub(hard, soft));
> - __hrtimer_start_range_ns(&rt_b->rt_period_timer, soft, delta,
> - HRTIMER_MODE_ABS_PINNED, 0);
> - }
> + start_bandwidth_timer(&rt_b->rt_period_timer, rt_b->rt_period);
> raw_spin_unlock(&rt_b->rt_runtime_lock);
> }
>
> @@ -241,6 +244,15 @@ struct cfs_rq;
>
> static LIST_HEAD(task_groups);
>
> +#ifdef CONFIG_CFS_BANDWIDTH
> +struct cfs_bandwidth {
> + raw_spinlock_t lock;
> + ktime_t period;
> + u64 runtime, quota;
> + struct hrtimer period_timer;
> +};
> +#endif
> +
> /* task group related information */
> struct task_group {
> #ifdef CONFIG_CGROUP_SCHED
> @@ -272,6 +284,10 @@ struct task_group {
> struct task_group *parent;
> struct list_head siblings;
> struct list_head children;
> +
> +#ifdef CONFIG_CFS_BANDWIDTH
> + struct cfs_bandwidth cfs_bandwidth;
> +#endif
> };
>
> #ifdef CONFIG_USER_SCHED
> @@ -445,9 +461,76 @@ struct cfs_rq {
> */
> unsigned long rq_weight;
> #endif
> +#ifdef CONFIG_CFS_BANDWIDTH
> + u64 quota_assigned, quota_used;
> +#endif
> #endif
> };
>
> +#ifdef CONFIG_CFS_BANDWIDTH
> +static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun);
> +
> +static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> +{
> + struct cfs_bandwidth *cfs_b =
> + container_of(timer, struct cfs_bandwidth, period_timer);
> + ktime_t now;
> + int overrun;
> + int idle = 0;
> +
> + for (;;) {
> + now = hrtimer_cb_get_time(timer);
> + overrun = hrtimer_forward(timer, now, cfs_b->period);
> +
> + if (!overrun)
> + break;
> +
> + idle = do_sched_cfs_period_timer(cfs_b, overrun);
> + }
> +
> + return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
> +}
> +
> +static
> +void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, u64 quota, u64 period)
> +{
> + raw_spin_lock_init(&cfs_b->lock);
> + cfs_b->quota = cfs_b->runtime = quota;
> + cfs_b->period = ns_to_ktime(period);
> +
> + hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + cfs_b->period_timer.function = sched_cfs_period_timer;
> +}
> +
> +static
> +void init_cfs_rq_quota(struct cfs_rq *cfs_rq)
> +{
> + cfs_rq->quota_used = 0;
> + if (cfs_rq->tg->cfs_bandwidth.quota == RUNTIME_INF)
> + cfs_rq->quota_assigned = RUNTIME_INF;
> + else
> + cfs_rq->quota_assigned = 0;
> +}
> +
> +static void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> +{
> + if (cfs_b->quota == RUNTIME_INF)
> + return;
> +
> + if (hrtimer_active(&cfs_b->period_timer))
> + return;
> +
> + raw_spin_lock(&cfs_b->lock);
> + start_bandwidth_timer(&cfs_b->period_timer, cfs_b->period);
> + raw_spin_unlock(&cfs_b->lock);
> +}
> +
> +static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> +{
> + hrtimer_cancel(&cfs_b->period_timer);
> +}
> +#endif
May be you could define some of this functions for !CONFIG_CFS_BANDWIDTH case
and avoid them calling under #ifdef ? I was given this comment during my
initial iterations.
> +
> /* Real-Time classes' related field in a runqueue: */
> struct rt_rq {
> struct rt_prio_array active;
> @@ -1834,6 +1917,14 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
> #endif
> }
>
> +#ifdef CONFIG_CFS_BANDWIDTH
> +/*
> + * default period for cfs group bandwidth.
> + * default: 0.5s
> + */
> +static u64 sched_cfs_bandwidth_period = 500000000ULL;
> +#endif
> +
> #include "sched_stats.h"
> #include "sched_idletask.c"
> #include "sched_fair.c"
> @@ -9422,6 +9513,9 @@ static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
> tg->cfs_rq[cpu] = cfs_rq;
> init_cfs_rq(cfs_rq, rq);
> cfs_rq->tg = tg;
> +#ifdef CONFIG_CFS_BANDWIDTH
> + init_cfs_rq_quota(cfs_rq);
> +#endif
> if (add)
> list_add(&cfs_rq->leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);
>
> @@ -9594,6 +9688,10 @@ void __init sched_init(void)
> * We achieve this by letting init_task_group's tasks sit
> * directly in rq->cfs (i.e init_task_group->se[] = NULL).
> */
> +#ifdef CONFIG_CFS_BANDWIDTH
> + init_cfs_bandwidth(&init_task_group.cfs_bandwidth,
> + RUNTIME_INF, sched_cfs_bandwidth_period);
> +#endif
> init_tg_cfs_entry(&init_task_group, &rq->cfs, NULL, i, 1, NULL);
> #elif defined CONFIG_USER_SCHED
> root_task_group.shares = NICE_0_LOAD;
> @@ -9851,6 +9949,10 @@ static void free_fair_sched_group(struct task_group *tg)
> {
> int i;
>
> +#ifdef CONFIG_CFS_BANDWIDTH
> + destroy_cfs_bandwidth(&tg->cfs_bandwidth);
> +#endif
> +
> for_each_possible_cpu(i) {
> if (tg->cfs_rq)
> kfree(tg->cfs_rq[i]);
> @@ -9878,7 +9980,10 @@ int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
> goto err;
>
> tg->shares = NICE_0_LOAD;
> -
> +#ifdef CONFIG_CFS_BANDWIDTH
> + init_cfs_bandwidth(&tg->cfs_bandwidth, RUNTIME_INF,
> + sched_cfs_bandwidth_period);
> +#endif
> for_each_possible_cpu(i) {
> rq = cpu_rq(i);
>
> @@ -10333,7 +10438,7 @@ static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
> return walk_tg_tree(tg_schedulable, tg_nop, &data);
> }
>
> -static int tg_set_bandwidth(struct task_group *tg,
> +static int tg_set_rt_bandwidth(struct task_group *tg,
> u64 rt_period, u64 rt_runtime)
> {
> int i, err = 0;
> @@ -10372,7 +10477,7 @@ int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
> if (rt_runtime_us < 0)
> rt_runtime = RUNTIME_INF;
>
> - return tg_set_bandwidth(tg, rt_period, rt_runtime);
> + return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
> }
>
> long sched_group_rt_runtime(struct task_group *tg)
> @@ -10397,7 +10502,7 @@ int sched_group_set_rt_period(struct task_group *tg, long rt_period_us)
> if (rt_period == 0)
> return -EINVAL;
>
> - return tg_set_bandwidth(tg, rt_period, rt_runtime);
> + return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
> }
>
> long sched_group_rt_period(struct task_group *tg)
> @@ -10604,6 +10709,120 @@ static u64 cpu_shares_read_u64(struct cgroup *cgrp, struct cftype *cft)
>
> return (u64) tg->shares;
> }
> +
> +#ifdef CONFIG_CFS_BANDWIDTH
> +static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
> +{
> + int i;
> + static DEFINE_MUTEX(mutex);
> +
> + if (tg == &init_task_group)
> + return -EINVAL;
> +
> + if (!period)
> + return -EINVAL;
> +
> + mutex_lock(&mutex);
What is this mutex for ? So you essentially serializing the bandwidth
setting of all groups ? While that iself isn't an issue, just wondering if
cfs_bandwidth.lock isn't suffient ?
> + /*
> + * Ensure we have at least one tick of bandwidth every period. This is
> + * to prevent reaching a state of large arrears when throttled via
> + * entity_tick() resulting in prolonged exit starvation.
> + */
> + if (NS_TO_JIFFIES(quota) < 1)
> + return -EINVAL;
Return with mutex held ?
> +
> + raw_spin_lock_irq(&tg->cfs_bandwidth.lock);
> + tg->cfs_bandwidth.period = ns_to_ktime(period);
> + tg->cfs_bandwidth.runtime = tg->cfs_bandwidth.quota = quota;
> + raw_spin_unlock_irq(&tg->cfs_bandwidth.lock);
> +
> + for_each_possible_cpu(i) {
> + struct cfs_rq *cfs_rq = tg->cfs_rq[i];
> + struct rq *rq = rq_of(cfs_rq);
> +
> + raw_spin_lock_irq(&rq->lock);
> + cfs_rq->quota_used = 0;
> + if (quota == RUNTIME_INF)
> + cfs_rq->quota_assigned = RUNTIME_INF;
> + else
> + cfs_rq->quota_assigned = 0;
> + raw_spin_unlock_irq(&rq->lock);
> + }
> + mutex_unlock(&mutex);
> +
> + return 0;
> +}
> +
> static void task_waking_fair(struct rq *rq, struct task_struct *p)
> @@ -1172,7 +1180,7 @@ static void task_waking_fair(struct rq *rq, struct task_struct *p)
> * We still saw a performance dip, some tracing learned us that between
> * cgroup:/ and cgroup:/foo balancing the number of affine wakeups increased
> * significantly. Therefore try to bias the error in direction of failing
> - * the affine wakeup.
> + * the affie wakeup.
Unintended change ?
Regards,
Bharata.
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