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sched: simplify adaptive latency

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simplify adaptive latency.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Peter Zijlstra 2007-10-15 17:00:05 +02:00 committed by Ingo Molnar
parent 4d78e7b656
commit 6d0f0ebd06
1 changed files with 9 additions and 104 deletions
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113
kernel/sched_fair.c
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@ -217,77 +217,14 @@ static u64 __sched_period(unsigned long nr_running)
return period;
}
/*
* Calculate the preemption granularity needed to schedule every
* runnable task once per sysctl_sched_latency amount of time.
* (down to a sensible low limit on granularity)
*
* For example, if there are 2 tasks running and latency is 10 msecs,
* we switch tasks every 5 msecs. If we have 3 tasks running, we have
* to switch tasks every 3.33 msecs to get a 10 msecs observed latency
* for each task. We do finer and finer scheduling up to until we
* reach the minimum granularity value.
*
* To achieve this we use the following dynamic-granularity rule:
*
* gran = lat/nr - lat/nr/nr
*
* This comes out of the following equations:
*
* kA1 + gran = kB1
* kB2 + gran = kA2
* kA2 = kA1
* kB2 = kB1 - d + d/nr
* lat = d * nr
*
* Where 'k' is key, 'A' is task A (waiting), 'B' is task B (running),
* '1' is start of time, '2' is end of time, 'd' is delay between
* 1 and 2 (during which task B was running), 'nr' is number of tasks
* running, 'lat' is the the period of each task. ('lat' is the
* sched_latency that we aim for.)
*/
static long
sched_granularity(struct cfs_rq *cfs_rq)
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
unsigned int gran = sysctl_sched_latency;
unsigned int nr = cfs_rq->nr_running;
u64 period = __sched_period(cfs_rq->nr_running);
if (nr > 1) {
gran = gran/nr - gran/nr/nr;
gran = max(gran, sysctl_sched_min_granularity);
}
period *= se->load.weight;
do_div(period, cfs_rq->load.weight);
return gran;
}
/*
* We rescale the rescheduling granularity of tasks according to their
* nice level, but only linearly, not exponentially:
*/
static long
niced_granularity(struct sched_entity *curr, unsigned long granularity)
{
u64 tmp;
if (likely(curr->load.weight == NICE_0_LOAD))
return granularity;
/*
* Positive nice levels get the same granularity as nice-0:
*/
if (likely(curr->load.weight < NICE_0_LOAD)) {
tmp = curr->load.weight * (u64)granularity;
return (long) (tmp >> NICE_0_SHIFT);
}
/*
* Negative nice level tasks get linearly finer
* granularity:
*/
tmp = curr->load.inv_weight * (u64)granularity;
/*
* It will always fit into 'long':
*/
return (long) (tmp >> (WMULT_SHIFT-NICE_0_SHIFT));
return period;
}
static inline void
@ -646,36 +583,13 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
*/
static void
__check_preempt_curr_fair(struct cfs_rq *cfs_rq, struct sched_entity *se,
struct sched_entity *curr, unsigned long granularity)
struct sched_entity *curr)
{
s64 __delta = curr->fair_key - se->fair_key;
unsigned long ideal_runtime, delta_exec;
/*
* ideal_runtime is compared against sum_exec_runtime, which is
* walltime, hence do not scale.
*/
ideal_runtime = max(sysctl_sched_latency / cfs_rq->nr_running,
(unsigned long)sysctl_sched_min_granularity);
/*
* If we executed more than what the latency constraint suggests,
* reduce the rescheduling granularity. This way the total latency
* of how much a task is not scheduled converges to
* sysctl_sched_latency:
*/
ideal_runtime = sched_slice(cfs_rq, curr);
delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
if (delta_exec > ideal_runtime)
granularity = 0;
/*
* Take scheduling granularity into account - do not
* preempt the current task unless the best task has
* a larger than sched_granularity fairness advantage:
*
* scale granularity as key space is in fair_clock.
*/
if (__delta > niced_granularity(curr, granularity))
resched_task(rq_of(cfs_rq)->curr);
}
@ -749,8 +663,7 @@ static void entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
if (next == curr)
return;
__check_preempt_curr_fair(cfs_rq, next, curr,
sched_granularity(cfs_rq));
__check_preempt_curr_fair(cfs_rq, next, curr);
}
/**************************************************
@ -944,7 +857,6 @@ static void check_preempt_curr_fair(struct rq *rq, struct task_struct *p)
{
struct task_struct *curr = rq->curr;
struct cfs_rq *cfs_rq = task_cfs_rq(curr);
unsigned long gran;
if (unlikely(rt_prio(p->prio))) {
update_rq_clock(rq);
@ -953,15 +865,8 @@ static void check_preempt_curr_fair(struct rq *rq, struct task_struct *p)
return;
}
gran = sysctl_sched_wakeup_granularity;
/*
* Batch tasks prefer throughput over latency:
*/
if (unlikely(p->policy == SCHED_BATCH))
gran = sysctl_sched_batch_wakeup_granularity;
if (is_same_group(curr, p))
__check_preempt_curr_fair(cfs_rq, &p->se, &curr->se, gran);
__check_preempt_curr_fair(cfs_rq, &p->se, &curr->se);
}
static struct task_struct *pick_next_task_fair(struct rq *rq)