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Subject[PATCH v3 08/12] sched: move cfs task on a CPU with higher capacity
Date
If the CPU is used for handling lot of IRQs, trig a load balance to check if
it's worth moving its tasks on another CPU that has more capacity.

As a sidenote, this will note generate more spurious ilb because we already
trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that
has a task, we will trig the ilb once for migrating the task.

The nohz_kick_needed function has been cleaned up a bit while adding the new
test

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 58 +++++++++++++++++++++++++++++++++++++----------------
1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a23c938..742ad88 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5944,6 +5944,14 @@ static bool update_sd_pick_busiest(struct lb_env *env,
return true;
}

+ /*
+ * The group capacity is reduced probably because of activity from other
+ * sched class or interrupts which use part of the available capacity
+ */
+ if ((sg->sgc->capacity_orig * 100) > (sgs->group_capacity *
+ env->sd->imbalance_pct))
+ return true;
+
return false;
}

@@ -6421,13 +6429,24 @@ static int need_active_balance(struct lb_env *env)
struct sched_domain *sd = env->sd;

if (env->idle == CPU_NEWLY_IDLE) {
+ int src_cpu = env->src_cpu;

/*
* ASYM_PACKING needs to force migrate tasks from busy but
* higher numbered CPUs in order to pack all tasks in the
* lowest numbered CPUs.
*/
- if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu)
+ if ((sd->flags & SD_ASYM_PACKING) && src_cpu > env->dst_cpu)
+ return 1;
+
+ /*
+ * If the CPUs share their cache and the src_cpu's capacity is
+ * reduced because of other sched_class or IRQs, we trig an
+ * active balance to move the task
+ */
+ if ((sd->flags & SD_SHARE_PKG_RESOURCES)
+ && ((capacity_orig_of(src_cpu) * 100) > (capacity_of(src_cpu) *
+ sd->imbalance_pct)))
return 1;
}

@@ -6529,6 +6548,8 @@ redo:

schedstat_add(sd, lb_imbalance[idle], env.imbalance);

+ env.src_cpu = busiest->cpu;
+
ld_moved = 0;
if (busiest->nr_running > 1) {
/*
@@ -6538,7 +6559,6 @@ redo:
* correctly treated as an imbalance.
*/
env.flags |= LBF_ALL_PINNED;
- env.src_cpu = busiest->cpu;
env.src_rq = busiest;
env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running);

@@ -7233,9 +7253,10 @@ static inline int nohz_kick_needed(struct rq *rq)
struct sched_domain *sd;
struct sched_group_capacity *sgc;
int nr_busy, cpu = rq->cpu;
+ bool kick = false;

if (unlikely(rq->idle_balance))
- return 0;
+ return false;

/*
* We may be recently in ticked or tickless idle mode. At the first
@@ -7249,38 +7270,41 @@ static inline int nohz_kick_needed(struct rq *rq)
* balancing.
*/
if (likely(!atomic_read(&nohz.nr_cpus)))
- return 0;
+ return false;

if (time_before(now, nohz.next_balance))
- return 0;
+ return false;

if (rq->nr_running >= 2)
- goto need_kick;
+ return true;

rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_busy, cpu));
-
if (sd) {
sgc = sd->groups->sgc;
nr_busy = atomic_read(&sgc->nr_busy_cpus);

- if (nr_busy > 1)
- goto need_kick_unlock;
+ if (nr_busy > 1) {
+ kick = true;
+ goto unlock;
+ }
+
+ if ((rq->cfs.h_nr_running >= 1)
+ && ((rq->cpu_capacity * sd->imbalance_pct) <
+ (rq->cpu_capacity_orig * 100))) {
+ kick = true;
+ goto unlock;
+ }
}

sd = rcu_dereference(per_cpu(sd_asym, cpu));
-
if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
sched_domain_span(sd)) < cpu))
- goto need_kick_unlock;
+ kick = true;

+unlock:
rcu_read_unlock();
- return 0;
-
-need_kick_unlock:
- rcu_read_unlock();
-need_kick:
- return 1;
+ return kick;
}
#else
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
--
1.9.1


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