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Message-Id: <1406569906-9763-9-git-send-email-vincent.guittot@linaro.org>
Date: Mon, 28 Jul 2014 19:51:42 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: peterz@...radead.org, mingo@...nel.org,
linux-kernel@...r.kernel.org, preeti@...ux.vnet.ibm.com,
linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org
Cc: riel@...hat.com, Morten.Rasmussen@....com, efault@....de,
nicolas.pitre@...aro.org, linaro-kernel@...ts.linaro.org,
daniel.lezcano@...aro.org, dietmar.eggemann@....com,
Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v4 08/12] sched: move cfs task on a CPU with higher capacity
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@...aro.org>
---
kernel/sched/fair.c | 69 +++++++++++++++++++++++++++++++++++++----------------
1 file changed, 49 insertions(+), 20 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6843016..1cde8dd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5969,6 +5969,14 @@ 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;
}
@@ -6455,13 +6463,23 @@ 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 ((capacity_orig_of(src_cpu) * 100) > (capacity_of(src_cpu) *
+ sd->imbalance_pct))
return 1;
}
@@ -6563,6 +6581,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
schedstat_add(sd, lb_imbalance[idle], env.imbalance);
+ env.src_cpu = busiest->cpu;
+
ld_moved = 0;
if (busiest->nr_running > 1) {
/*
@@ -6572,7 +6592,6 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* 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);
@@ -7262,10 +7281,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
/*
* Current heuristic for kicking the idle load balancer in the presence
- * of an idle cpu is the system.
+ * of an idle cpu in the system.
* - This rq has more than one task.
- * - At any scheduler domain level, this cpu's scheduler group has multiple
- * busy cpu's exceeding the group's capacity.
+ * - This rq has at least one CFS task and the capacity of the CPU is
+ * significantly reduced because of RT tasks or IRQs.
+ * - At parent of LLC scheduler domain level, this cpu's scheduler group has
+ * multiple busy cpu.
* - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
* domain span are idle.
*/
@@ -7275,9 +7296,10 @@ 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
@@ -7291,38 +7313,45 @@ 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;
+ }
+
}
- sd = rcu_dereference(per_cpu(sd_asym, cpu));
+ sd = rcu_dereference(rq->sd);
+ if (sd) {
+ 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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