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sched/fair: Rework find_idlest_group()

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The slow wake up path computes per sched_group statisics to select the
idlest group, which is quite similar to what load_balance() is doing
for selecting busiest group. Rework find_idlest_group() to classify the
sched_group and select the idlest one following the same steps as
load_balance().

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hdanton@sina.com
Cc: parth@linux.ibm.com
Cc: pauld@redhat.com
Cc: quentin.perret@arm.com
Cc: riel@surriel.com
Cc: srikar@linux.vnet.ibm.com
Cc: valentin.schneider@arm.com
Link: https://lkml.kernel.org/r/1571405198-27570-12-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vincent Guittot 2019-10-18 15:26:38 +02:00 committed by Ingo Molnar
parent fc1273f4ce
commit 57abff067a
1 changed files with 256 additions and 128 deletions
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384
kernel/sched/fair.c
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@ -5531,127 +5531,9 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p,
return target;
}
static unsigned long cpu_util_without(int cpu, struct task_struct *p);
static unsigned long capacity_spare_without(int cpu, struct task_struct *p)
{
return max_t(long, capacity_of(cpu) - cpu_util_without(cpu, p), 0);
}
/*
* find_idlest_group finds and returns the least busy CPU group within the
* domain.
*
* Assumes p is allowed on at least one CPU in sd.
*/
static struct sched_group *
find_idlest_group(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int sd_flag)
{
struct sched_group *idlest = NULL, *group = sd->groups;
struct sched_group *most_spare_sg = NULL;
unsigned long min_load = ULONG_MAX, this_load = ULONG_MAX;
unsigned long most_spare = 0, this_spare = 0;
int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;
unsigned long imbalance = scale_load_down(NICE_0_LOAD) *
(sd->imbalance_pct-100) / 100;
do {
unsigned long load;
unsigned long spare_cap, max_spare_cap;
int local_group;
int i;
/* Skip over this group if it has no CPUs allowed */
if (!cpumask_intersects(sched_group_span(group),
p->cpus_ptr))
continue;
local_group = cpumask_test_cpu(this_cpu,
sched_group_span(group));
/*
* Tally up the load of all CPUs in the group and find
* the group containing the CPU with most spare capacity.
*/
load = 0;
max_spare_cap = 0;
for_each_cpu(i, sched_group_span(group)) {
load += cpu_load(cpu_rq(i));
spare_cap = capacity_spare_without(i, p);
if (spare_cap > max_spare_cap)
max_spare_cap = spare_cap;
}
/* Adjust by relative CPU capacity of the group */
load = (load * SCHED_CAPACITY_SCALE) /
group->sgc->capacity;
if (local_group) {
this_load = load;
this_spare = max_spare_cap;
} else {
if (load < min_load) {
min_load = load;
idlest = group;
}
if (most_spare < max_spare_cap) {
most_spare = max_spare_cap;
most_spare_sg = group;
}
}
} while (group = group->next, group != sd->groups);
/*
* The cross-over point between using spare capacity or least load
* is too conservative for high utilization tasks on partially
* utilized systems if we require spare_capacity > task_util(p),
* so we allow for some task stuffing by using
* spare_capacity > task_util(p)/2.
*
* Spare capacity can't be used for fork because the utilization has
* not been set yet, we must first select a rq to compute the initial
* utilization.
*/
if (sd_flag & SD_BALANCE_FORK)
goto skip_spare;
if (this_spare > task_util(p) / 2 &&
imbalance_scale*this_spare > 100*most_spare)
return NULL;
if (most_spare > task_util(p) / 2)
return most_spare_sg;
skip_spare:
if (!idlest)
return NULL;
/*
* When comparing groups across NUMA domains, it's possible for the
* local domain to be very lightly loaded relative to the remote
* domains but "imbalance" skews the comparison making remote CPUs
* look much more favourable. When considering cross-domain, add
* imbalance to the load on the remote node and consider staying
* local.
*/
if ((sd->flags & SD_NUMA) &&
min_load + imbalance >= this_load)
return NULL;
if (min_load >= this_load + imbalance)
return NULL;
if ((this_load < (min_load + imbalance)) &&
(100*this_load < imbalance_scale*min_load))
return NULL;
return idlest;
}
int this_cpu, int sd_flag);
/*
* find_idlest_group_cpu - find the idlest CPU among the CPUs in the group.
@ -5724,7 +5606,7 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
return prev_cpu;
/*
* We need task's util for capacity_spare_without, sync it up to
* We need task's util for cpu_util_without, sync it up to
* prev_cpu's last_update_time.
*/
if (!(sd_flag & SD_BALANCE_FORK))
@ -7905,13 +7787,13 @@ static inline int sg_imbalanced(struct sched_group *group)
* any benefit for the load balance.
*/
static inline bool
group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
{
if (sgs->sum_nr_running < sgs->group_weight)
return true;
if ((sgs->group_capacity * 100) >
(sgs->group_util * env->sd->imbalance_pct))
(sgs->group_util * imbalance_pct))
return true;
return false;
@ -7926,13 +7808,13 @@ group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
* false.
*/
static inline bool
group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
{
if (sgs->sum_nr_running <= sgs->group_weight)
return false;
if ((sgs->group_capacity * 100) <
(sgs->group_util * env->sd->imbalance_pct))
(sgs->group_util * imbalance_pct))
return true;
return false;
@ -7959,11 +7841,11 @@ group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
}
static inline enum
group_type group_classify(struct lb_env *env,
group_type group_classify(unsigned int imbalance_pct,
struct sched_group *group,
struct sg_lb_stats *sgs)
{
if (group_is_overloaded(env, sgs))
if (group_is_overloaded(imbalance_pct, sgs))
return group_overloaded;
if (sg_imbalanced(group))
@ -7975,7 +7857,7 @@ group_type group_classify(struct lb_env *env,
if (sgs->group_misfit_task_load)
return group_misfit_task;
if (!group_has_capacity(env, sgs))
if (!group_has_capacity(imbalance_pct, sgs))
return group_fully_busy;
return group_has_spare;
@ -8076,7 +7958,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
sgs->group_weight = group->group_weight;
sgs->group_type = group_classify(env, group, sgs);
sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs);
/* Computing avg_load makes sense only when group is overloaded */
if (sgs->group_type == group_overloaded)
@ -8231,6 +8113,252 @@ static inline enum fbq_type fbq_classify_rq(struct rq *rq)
}
#endif /* CONFIG_NUMA_BALANCING */
struct sg_lb_stats;
/*
* update_sg_wakeup_stats - Update sched_group's statistics for wakeup.
* @denv: The ched_domain level to look for idlest group.
* @group: sched_group whose statistics are to be updated.
* @sgs: variable to hold the statistics for this group.
*/
static inline void update_sg_wakeup_stats(struct sched_domain *sd,
struct sched_group *group,
struct sg_lb_stats *sgs,
struct task_struct *p)
{
int i, nr_running;
memset(sgs, 0, sizeof(*sgs));
for_each_cpu(i, sched_group_span(group)) {
struct rq *rq = cpu_rq(i);
sgs->group_load += cpu_load(rq);
sgs->group_util += cpu_util_without(i, p);
sgs->sum_h_nr_running += rq->cfs.h_nr_running;
nr_running = rq->nr_running;
sgs->sum_nr_running += nr_running;
/*
* No need to call idle_cpu() if nr_running is not 0
*/
if (!nr_running && idle_cpu(i))
sgs->idle_cpus++;
}
/* Check if task fits in the group */
if (sd->flags & SD_ASYM_CPUCAPACITY &&
!task_fits_capacity(p, group->sgc->max_capacity)) {
sgs->group_misfit_task_load = 1;
}
sgs->group_capacity = group->sgc->capacity;
sgs->group_type = group_classify(sd->imbalance_pct, group, sgs);
/*
* Computing avg_load makes sense only when group is fully busy or
* overloaded
*/
if (sgs->group_type < group_fully_busy)
sgs->avg_load = (sgs->group_load * SCHED_CAPACITY_SCALE) /
sgs->group_capacity;
}
static bool update_pick_idlest(struct sched_group *idlest,
struct sg_lb_stats *idlest_sgs,
struct sched_group *group,
struct sg_lb_stats *sgs)
{
if (sgs->group_type < idlest_sgs->group_type)
return true;
if (sgs->group_type > idlest_sgs->group_type)
return false;
/*
* The candidate and the current idlest group are the same type of
* group. Let check which one is the idlest according to the type.
*/
switch (sgs->group_type) {
case group_overloaded:
case group_fully_busy:
/* Select the group with lowest avg_load. */
if (idlest_sgs->avg_load <= sgs->avg_load)
return false;
break;
case group_imbalanced:
case group_asym_packing:
/* Those types are not used in the slow wakeup path */
return false;
case group_misfit_task:
/* Select group with the highest max capacity */
if (idlest->sgc->max_capacity >= group->sgc->max_capacity)
return false;
break;
case group_has_spare:
/* Select group with most idle CPUs */
if (idlest_sgs->idle_cpus >= sgs->idle_cpus)
return false;
break;
}
return true;
}
/*
* find_idlest_group() finds and returns the least busy CPU group within the
* domain.
*
* Assumes p is allowed on at least one CPU in sd.
*/
static struct sched_group *
find_idlest_group(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int sd_flag)
{
struct sched_group *idlest = NULL, *local = NULL, *group = sd->groups;
struct sg_lb_stats local_sgs, tmp_sgs;
struct sg_lb_stats *sgs;
unsigned long imbalance;
struct sg_lb_stats idlest_sgs = {
.avg_load = UINT_MAX,
.group_type = group_overloaded,
};
imbalance = scale_load_down(NICE_0_LOAD) *
(sd->imbalance_pct-100) / 100;
do {
int local_group;
/* Skip over this group if it has no CPUs allowed */
if (!cpumask_intersects(sched_group_span(group),
p->cpus_ptr))
continue;
local_group = cpumask_test_cpu(this_cpu,
sched_group_span(group));
if (local_group) {
sgs = &local_sgs;
local = group;
} else {
sgs = &tmp_sgs;
}
update_sg_wakeup_stats(sd, group, sgs, p);
if (!local_group && update_pick_idlest(idlest, &idlest_sgs, group, sgs)) {
idlest = group;
idlest_sgs = *sgs;
}
} while (group = group->next, group != sd->groups);
/* There is no idlest group to push tasks to */
if (!idlest)
return NULL;
/*
* If the local group is idler than the selected idlest group
* don't try and push the task.
*/
if (local_sgs.group_type < idlest_sgs.group_type)
return NULL;
/*
* If the local group is busier than the selected idlest group
* try and push the task.
*/
if (local_sgs.group_type > idlest_sgs.group_type)
return idlest;
switch (local_sgs.group_type) {
case group_overloaded:
case group_fully_busy:
/*
* When comparing groups across NUMA domains, it's possible for
* the local domain to be very lightly loaded relative to the
* remote domains but "imbalance" skews the comparison making
* remote CPUs look much more favourable. When considering
* cross-domain, add imbalance to the load on the remote node
* and consider staying local.
*/
if ((sd->flags & SD_NUMA) &&
((idlest_sgs.avg_load + imbalance) >= local_sgs.avg_load))
return NULL;
/*
* If the local group is less loaded than the selected
* idlest group don't try and push any tasks.
*/
if (idlest_sgs.avg_load >= (local_sgs.avg_load + imbalance))
return NULL;
if (100 * local_sgs.avg_load <= sd->imbalance_pct * idlest_sgs.avg_load)
return NULL;
break;
case group_imbalanced:
case group_asym_packing:
/* Those type are not used in the slow wakeup path */
return NULL;
case group_misfit_task:
/* Select group with the highest max capacity */
if (local->sgc->max_capacity >= idlest->sgc->max_capacity)
return NULL;
break;
case group_has_spare:
if (sd->flags & SD_NUMA) {
#ifdef CONFIG_NUMA_BALANCING
int idlest_cpu;
/*
* If there is spare capacity at NUMA, try to select
* the preferred node
*/
if (cpu_to_node(this_cpu) == p->numa_preferred_nid)
return NULL;
idlest_cpu = cpumask_first(sched_group_span(idlest));
if (cpu_to_node(idlest_cpu) == p->numa_preferred_nid)
return idlest;
#endif
/*
* Otherwise, keep the task on this node to stay close
* its wakeup source and improve locality. If there is
* a real need of migration, periodic load balance will
* take care of it.
*/
if (local_sgs.idle_cpus)
return NULL;
}
/*
* Select group with highest number of idle CPUs. We could also
* compare the utilization which is more stable but it can end
* up that the group has less spare capacity but finally more
* idle CPUs which means more opportunity to run task.
*/
if (local_sgs.idle_cpus >= idlest_sgs.idle_cpus)
return NULL;
break;
}
return idlest;
}
/**
* update_sd_lb_stats - Update sched_domain's statistics for load balancing.
* @env: The load balancing environment.