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sched: de-SCHED_OTHER-ize the RT path
The current wake-up code path tries to determine if it can optimize the wake-up to "this_cpu" by computing load calculations. The problem is that these calculations are only relevant to SCHED_OTHER tasks where load is king. For RT tasks, priority is king. So the load calculation is completely wasted bandwidth. Therefore, we create a new sched_class interface to help with pre-wakeup routing decisions and move the load calculation as a function of CFS task's class. Signed-off-by: Gregory Haskins <ghaskins@novell.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Gregory Haskins
Ingo Molnar
parent
697f0a487f
commit
e7693a362e
5 changed files with 195 additions and 140 deletions
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@ -827,6 +827,7 @@ struct sched_class {
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void (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup);
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void (*dequeue_task) (struct rq *rq, struct task_struct *p, int sleep);
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void (*yield_task) (struct rq *rq);
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int (*select_task_rq)(struct task_struct *p, int sync);
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void (*check_preempt_curr) (struct rq *rq, struct task_struct *p);
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167
kernel/sched.c
167
kernel/sched.c
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@ -960,6 +960,13 @@ static inline void dec_cpu_load(struct rq *rq, unsigned long load)
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update_load_sub(&rq->load, load);
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}
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#ifdef CONFIG_SMP
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static unsigned long source_load(int cpu, int type);
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static unsigned long target_load(int cpu, int type);
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static unsigned long cpu_avg_load_per_task(int cpu);
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static int task_hot(struct task_struct *p, u64 now, struct sched_domain *sd);
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#endif /* CONFIG_SMP */
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#include "sched_stats.h"
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#include "sched_idletask.c"
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#include "sched_fair.c"
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@ -1118,7 +1125,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
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/*
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* Is this task likely cache-hot:
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*/
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static inline int
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static int
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task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
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{
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s64 delta;
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@ -1343,7 +1350,7 @@ static unsigned long target_load(int cpu, int type)
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/*
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* Return the average load per task on the cpu's run queue
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*/
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static inline unsigned long cpu_avg_load_per_task(int cpu)
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static unsigned long cpu_avg_load_per_task(int cpu)
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{
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struct rq *rq = cpu_rq(cpu);
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unsigned long total = weighted_cpuload(cpu);
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@ -1500,58 +1507,6 @@ static int sched_balance_self(int cpu, int flag)
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#endif /* CONFIG_SMP */
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/*
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* wake_idle() will wake a task on an idle cpu if task->cpu is
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* not idle and an idle cpu is available. The span of cpus to
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* search starts with cpus closest then further out as needed,
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* so we always favor a closer, idle cpu.
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*
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* Returns the CPU we should wake onto.
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*/
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#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
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static int wake_idle(int cpu, struct task_struct *p)
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{
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cpumask_t tmp;
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struct sched_domain *sd;
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int i;
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/*
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* If it is idle, then it is the best cpu to run this task.
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*
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* This cpu is also the best, if it has more than one task already.
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* Siblings must be also busy(in most cases) as they didn't already
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* pickup the extra load from this cpu and hence we need not check
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* sibling runqueue info. This will avoid the checks and cache miss
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* penalities associated with that.
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*/
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if (idle_cpu(cpu) || cpu_rq(cpu)->nr_running > 1)
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return cpu;
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for_each_domain(cpu, sd) {
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if (sd->flags & SD_WAKE_IDLE) {
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cpus_and(tmp, sd->span, p->cpus_allowed);
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for_each_cpu_mask(i, tmp) {
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if (idle_cpu(i)) {
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if (i != task_cpu(p)) {
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schedstat_inc(p,
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se.nr_wakeups_idle);
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}
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return i;
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}
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}
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} else {
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break;
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}
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}
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return cpu;
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}
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#else
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static inline int wake_idle(int cpu, struct task_struct *p)
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{
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return cpu;
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}
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#endif
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/***
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* try_to_wake_up - wake up a thread
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* @p: the to-be-woken-up thread
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@ -1573,8 +1528,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
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long old_state;
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struct rq *rq;
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#ifdef CONFIG_SMP
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struct sched_domain *sd, *this_sd = NULL;
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unsigned long load, this_load;
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int new_cpu;
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#endif
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@ -1594,90 +1547,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
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if (unlikely(task_running(rq, p)))
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goto out_activate;
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new_cpu = cpu;
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schedstat_inc(rq, ttwu_count);
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if (cpu == this_cpu) {
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schedstat_inc(rq, ttwu_local);
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goto out_set_cpu;
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}
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for_each_domain(this_cpu, sd) {
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if (cpu_isset(cpu, sd->span)) {
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schedstat_inc(sd, ttwu_wake_remote);
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this_sd = sd;
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break;
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}
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}
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if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
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goto out_set_cpu;
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/*
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* Check for affine wakeup and passive balancing possibilities.
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*/
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if (this_sd) {
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int idx = this_sd->wake_idx;
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unsigned int imbalance;
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imbalance = 100 + (this_sd->imbalance_pct - 100) / 2;
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load = source_load(cpu, idx);
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this_load = target_load(this_cpu, idx);
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new_cpu = this_cpu; /* Wake to this CPU if we can */
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if (this_sd->flags & SD_WAKE_AFFINE) {
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unsigned long tl = this_load;
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unsigned long tl_per_task;
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/*
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* Attract cache-cold tasks on sync wakeups:
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*/
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if (sync && !task_hot(p, rq->clock, this_sd))
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goto out_set_cpu;
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schedstat_inc(p, se.nr_wakeups_affine_attempts);
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tl_per_task = cpu_avg_load_per_task(this_cpu);
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/*
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* If sync wakeup then subtract the (maximum possible)
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* effect of the currently running task from the load
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* of the current CPU:
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*/
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if (sync)
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tl -= current->se.load.weight;
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if ((tl <= load &&
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tl + target_load(cpu, idx) <= tl_per_task) ||
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100*(tl + p->se.load.weight) <= imbalance*load) {
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/*
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* This domain has SD_WAKE_AFFINE and
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* p is cache cold in this domain, and
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* there is no bad imbalance.
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*/
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schedstat_inc(this_sd, ttwu_move_affine);
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schedstat_inc(p, se.nr_wakeups_affine);
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goto out_set_cpu;
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}
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}
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/*
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* Start passive balancing when half the imbalance_pct
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* limit is reached.
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*/
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if (this_sd->flags & SD_WAKE_BALANCE) {
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if (imbalance*this_load <= 100*load) {
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schedstat_inc(this_sd, ttwu_move_balance);
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schedstat_inc(p, se.nr_wakeups_passive);
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goto out_set_cpu;
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}
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}
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}
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new_cpu = cpu; /* Could not wake to this_cpu. Wake to cpu instead */
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out_set_cpu:
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new_cpu = wake_idle(new_cpu, p);
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new_cpu = p->sched_class->select_task_rq(p, sync);
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if (new_cpu != cpu) {
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set_task_cpu(p, new_cpu);
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task_rq_unlock(rq, &flags);
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@ -1693,6 +1563,23 @@ out_set_cpu:
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cpu = task_cpu(p);
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}
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#ifdef CONFIG_SCHEDSTATS
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schedstat_inc(rq, ttwu_count);
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if (cpu == this_cpu)
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schedstat_inc(rq, ttwu_local);
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else {
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struct sched_domain *sd;
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for_each_domain(this_cpu, sd) {
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if (cpu_isset(cpu, sd->span)) {
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schedstat_inc(sd, ttwu_wake_remote);
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break;
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}
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}
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}
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#endif
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out_activate:
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#endif /* CONFIG_SMP */
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schedstat_inc(p, se.nr_wakeups);
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@ -860,6 +860,151 @@ static void yield_task_fair(struct rq *rq)
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se->vruntime = rightmost->vruntime + 1;
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}
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/*
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* wake_idle() will wake a task on an idle cpu if task->cpu is
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* not idle and an idle cpu is available. The span of cpus to
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* search starts with cpus closest then further out as needed,
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* so we always favor a closer, idle cpu.
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*
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* Returns the CPU we should wake onto.
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*/
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#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
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static int wake_idle(int cpu, struct task_struct *p)
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{
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cpumask_t tmp;
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struct sched_domain *sd;
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int i;
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/*
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* If it is idle, then it is the best cpu to run this task.
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*
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* This cpu is also the best, if it has more than one task already.
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* Siblings must be also busy(in most cases) as they didn't already
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* pickup the extra load from this cpu and hence we need not check
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* sibling runqueue info. This will avoid the checks and cache miss
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* penalities associated with that.
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*/
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if (idle_cpu(cpu) || cpu_rq(cpu)->nr_running > 1)
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return cpu;
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for_each_domain(cpu, sd) {
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if (sd->flags & SD_WAKE_IDLE) {
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cpus_and(tmp, sd->span, p->cpus_allowed);
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for_each_cpu_mask(i, tmp) {
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if (idle_cpu(i)) {
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if (i != task_cpu(p)) {
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schedstat_inc(p,
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se.nr_wakeups_idle);
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}
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return i;
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}
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}
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} else {
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break;
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}
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}
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return cpu;
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}
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#else
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static inline int wake_idle(int cpu, struct task_struct *p)
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{
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return cpu;
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}
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#endif
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#ifdef CONFIG_SMP
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static int select_task_rq_fair(struct task_struct *p, int sync)
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{
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int cpu, this_cpu;
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struct rq *rq;
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struct sched_domain *sd, *this_sd = NULL;
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int new_cpu;
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cpu = task_cpu(p);
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rq = task_rq(p);
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this_cpu = smp_processor_id();
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new_cpu = cpu;
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for_each_domain(this_cpu, sd) {
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if (cpu_isset(cpu, sd->span)) {
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this_sd = sd;
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break;
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}
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}
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if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
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goto out_set_cpu;
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/*
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* Check for affine wakeup and passive balancing possibilities.
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*/
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if (this_sd) {
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int idx = this_sd->wake_idx;
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unsigned int imbalance;
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unsigned long load, this_load;
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imbalance = 100 + (this_sd->imbalance_pct - 100) / 2;
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load = source_load(cpu, idx);
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this_load = target_load(this_cpu, idx);
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new_cpu = this_cpu; /* Wake to this CPU if we can */
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if (this_sd->flags & SD_WAKE_AFFINE) {
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unsigned long tl = this_load;
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unsigned long tl_per_task;
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/*
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* Attract cache-cold tasks on sync wakeups:
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*/
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if (sync && !task_hot(p, rq->clock, this_sd))
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goto out_set_cpu;
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schedstat_inc(p, se.nr_wakeups_affine_attempts);
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tl_per_task = cpu_avg_load_per_task(this_cpu);
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/*
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* If sync wakeup then subtract the (maximum possible)
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* effect of the currently running task from the load
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* of the current CPU:
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*/
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if (sync)
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tl -= current->se.load.weight;
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if ((tl <= load &&
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tl + target_load(cpu, idx) <= tl_per_task) ||
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100*(tl + p->se.load.weight) <= imbalance*load) {
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/*
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* This domain has SD_WAKE_AFFINE and
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* p is cache cold in this domain, and
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* there is no bad imbalance.
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*/
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schedstat_inc(this_sd, ttwu_move_affine);
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schedstat_inc(p, se.nr_wakeups_affine);
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goto out_set_cpu;
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}
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}
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/*
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* Start passive balancing when half the imbalance_pct
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* limit is reached.
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*/
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if (this_sd->flags & SD_WAKE_BALANCE) {
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if (imbalance*this_load <= 100*load) {
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schedstat_inc(this_sd, ttwu_move_balance);
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schedstat_inc(p, se.nr_wakeups_passive);
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goto out_set_cpu;
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}
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}
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}
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new_cpu = cpu; /* Could not wake to this_cpu. Wake to cpu instead */
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out_set_cpu:
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return wake_idle(new_cpu, p);
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}
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#endif /* CONFIG_SMP */
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/*
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* Preempt the current task with a newly woken task if needed:
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*/
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@ -1153,6 +1298,9 @@ static const struct sched_class fair_sched_class = {
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.enqueue_task = enqueue_task_fair,
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.dequeue_task = dequeue_task_fair,
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.yield_task = yield_task_fair,
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#ifdef CONFIG_SMP
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.select_task_rq = select_task_rq_fair,
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#endif /* CONFIG_SMP */
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.check_preempt_curr = check_preempt_wakeup,
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@ -5,6 +5,12 @@
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* handled in sched_fair.c)
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*/
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#ifdef CONFIG_SMP
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static int select_task_rq_idle(struct task_struct *p, int sync)
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{
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return task_cpu(p); /* IDLE tasks as never migrated */
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}
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#endif /* CONFIG_SMP */
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/*
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* Idle tasks are unconditionally rescheduled:
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*/
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@ -72,6 +78,9 @@ const struct sched_class idle_sched_class = {
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/* dequeue is not valid, we print a debug message there: */
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.dequeue_task = dequeue_task_idle,
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#ifdef CONFIG_SMP
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.select_task_rq = select_task_rq_idle,
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#endif /* CONFIG_SMP */
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.check_preempt_curr = check_preempt_curr_idle,
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@ -150,6 +150,13 @@ yield_task_rt(struct rq *rq)
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requeue_task_rt(rq, rq->curr);
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}
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#ifdef CONFIG_SMP
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static int select_task_rq_rt(struct task_struct *p, int sync)
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{
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return task_cpu(p);
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}
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#endif /* CONFIG_SMP */
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/*
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* Preempt the current task with a newly woken task if needed:
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*/
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@ -667,6 +674,9 @@ const struct sched_class rt_sched_class = {
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.enqueue_task = enqueue_task_rt,
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.dequeue_task = dequeue_task_rt,
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.yield_task = yield_task_rt,
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#ifdef CONFIG_SMP
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.select_task_rq = select_task_rq_rt,
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#endif /* CONFIG_SMP */
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.check_preempt_curr = check_preempt_curr_rt,
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