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Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse Source 
Pull scheduler fixes from Ingo Molnar:
 "Three fixes that address an SMP balancing performance regression"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/core: Ensure load_balance() respects the active_mask
  sched/core: Address more wake_affine() regressions
  sched/core: Fix wake_affine() performance regression
This commit is contained in:
Linus Torvalds 2017-10-14 15:20:38 -04:00
commit a339b35130
3 changed files with 49 additions and 102 deletions
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8
include/linux/sched/topology.h
View File

@ -71,14 +71,6 @@ struct sched_domain_shared {
atomic_t ref;
atomic_t nr_busy_cpus;
int has_idle_cores;
/*
* Some variables from the most recent sd_lb_stats for this domain,
* used by wake_affine().
*/
unsigned long nr_running;
unsigned long load;
unsigned long capacity;
};
struct sched_domain {

140
kernel/sched/fair.c
View File

@ -5356,91 +5356,62 @@ static int wake_wide(struct task_struct *p)
return 1;
}
struct llc_stats {
unsigned long nr_running;
unsigned long load;
unsigned long capacity;
int has_capacity;
};
/*
* The purpose of wake_affine() is to quickly determine on which CPU we can run
* soonest. For the purpose of speed we only consider the waking and previous
* CPU.
*
* wake_affine_idle() - only considers 'now', it check if the waking CPU is (or
* will be) idle.
*
* wake_affine_weight() - considers the weight to reflect the average
* scheduling latency of the CPUs. This seems to work
* for the overloaded case.
*/
static bool get_llc_stats(struct llc_stats *stats, int cpu)
static bool
wake_affine_idle(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int prev_cpu, int sync)
{
struct sched_domain_shared *sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
if (idle_cpu(this_cpu))
return true;
if (!sds)
return false;
if (sync && cpu_rq(this_cpu)->nr_running == 1)
return true;
stats->nr_running = READ_ONCE(sds->nr_running);
stats->load = READ_ONCE(sds->load);
stats->capacity = READ_ONCE(sds->capacity);
stats->has_capacity = stats->nr_running < per_cpu(sd_llc_size, cpu);
return true;
return false;
}
/*
* Can a task be moved from prev_cpu to this_cpu without causing a load
* imbalance that would trigger the load balancer?
*
* Since we're running on 'stale' values, we might in fact create an imbalance
* but recomputing these values is expensive, as that'd mean iteration 2 cache
* domains worth of CPUs.
*/
static bool
wake_affine_llc(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int prev_cpu, int sync)
wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int prev_cpu, int sync)
{
struct llc_stats prev_stats, this_stats;
s64 this_eff_load, prev_eff_load;
unsigned long task_load;
if (!get_llc_stats(&prev_stats, prev_cpu) ||
!get_llc_stats(&this_stats, this_cpu))
return false;
this_eff_load = target_load(this_cpu, sd->wake_idx);
prev_eff_load = source_load(prev_cpu, sd->wake_idx);
/*
* If sync wakeup then subtract the (maximum possible)
* effect of the currently running task from the load
* of the current LLC.
*/
if (sync) {
unsigned long current_load = task_h_load(current);
/* in this case load hits 0 and this LLC is considered 'idle' */
if (current_load > this_stats.load)
if (current_load > this_eff_load)
return true;
this_stats.load -= current_load;
this_eff_load -= current_load;
}
/*
* The has_capacity stuff is not SMT aware, but by trying to balance
* the nr_running on both ends we try and fill the domain at equal
* rates, thereby first consuming cores before siblings.
*/
/* if the old cache has capacity, stay there */
if (prev_stats.has_capacity && prev_stats.nr_running < this_stats.nr_running+1)
return false;
/* if this cache has capacity, come here */
if (this_stats.has_capacity && this_stats.nr_running+1 < prev_stats.nr_running)
return true;
/*
* Check to see if we can move the load without causing too much
* imbalance.
*/
task_load = task_h_load(p);
this_eff_load = 100;
this_eff_load *= prev_stats.capacity;
this_eff_load += task_load;
if (sched_feat(WA_BIAS))
this_eff_load *= 100;
this_eff_load *= capacity_of(prev_cpu);
prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
prev_eff_load *= this_stats.capacity;
this_eff_load *= this_stats.load + task_load;
prev_eff_load *= prev_stats.load - task_load;
prev_eff_load -= task_load;
if (sched_feat(WA_BIAS))
prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
prev_eff_load *= capacity_of(this_cpu);
return this_eff_load <= prev_eff_load;
}
@ -5449,22 +5420,13 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p,
int prev_cpu, int sync)
{
int this_cpu = smp_processor_id();
bool affine;
bool affine = false;
/*
* Default to no affine wakeups; wake_affine() should not effect a task
* placement the load-balancer feels inclined to undo. The conservative
* option is therefore to not move tasks when they wake up.
*/
affine = false;
if (sched_feat(WA_IDLE) && !affine)
affine = wake_affine_idle(sd, p, this_cpu, prev_cpu, sync);
/*
* If the wakeup is across cache domains, try to evaluate if movement
* makes sense, otherwise rely on select_idle_siblings() to do
* placement inside the cache domain.
*/
if (!cpus_share_cache(prev_cpu, this_cpu))
affine = wake_affine_llc(sd, p, this_cpu, prev_cpu, sync);
if (sched_feat(WA_WEIGHT) && !affine)
affine = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);
schedstat_inc(p->se.statistics.nr_wakeups_affine_attempts);
if (affine) {
@ -7600,7 +7562,6 @@ static inline enum fbq_type fbq_classify_rq(struct rq *rq)
*/
static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
{
struct sched_domain_shared *shared = env->sd->shared;
struct sched_domain *child = env->sd->child;
struct sched_group *sg = env->sd->groups;
struct sg_lb_stats *local = &sds->local_stat;
@ -7672,22 +7633,6 @@ next_group:
if (env->dst_rq->rd->overload != overload)
env->dst_rq->rd->overload = overload;
}
if (!shared)
return;
/*
* Since these are sums over groups they can contain some CPUs
* multiple times for the NUMA domains.
*
* Currently only wake_affine_llc() and find_busiest_group()
* uses these numbers, only the last is affected by this problem.
*
* XXX fix that.
*/
WRITE_ONCE(shared->nr_running, sds->total_running);
WRITE_ONCE(shared->load, sds->total_load);
WRITE_ONCE(shared->capacity, sds->total_capacity);
}
/**
@ -8097,6 +8042,13 @@ static int should_we_balance(struct lb_env *env)
struct sched_group *sg = env->sd->groups;
int cpu, balance_cpu = -1;
/*
* Ensure the balancing environment is consistent; can happen
* when the softirq triggers 'during' hotplug.
*/
if (!cpumask_test_cpu(env->dst_cpu, env->cpus))
return 0;
/*
* In the newly idle case, we will allow all the cpu's
* to do the newly idle load balance.

3
kernel/sched/features.h
View File

@ -81,3 +81,6 @@ SCHED_FEAT(RT_RUNTIME_SHARE, true)
SCHED_FEAT(LB_MIN, false)
SCHED_FEAT(ATTACH_AGE_LOAD, true)
SCHED_FEAT(WA_IDLE, true)
SCHED_FEAT(WA_WEIGHT, true)
SCHED_FEAT(WA_BIAS, true)