While looking for idle CPUs for a waking task, we should also account
for the delays caused due to the bandwidth reduction by RT/IRQ tasks.
This patch does that by trying to find a higher capacity CPU with
minimum wake up latency.
Signed-off-by: Rohit Jain <rohit.k.j...@oracle.com>
---
kernel/sched/fair.c | 27 ++++++++++++++++++++++++---
1 file changed, 24 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0107280..eaede50 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5579,6 +5579,11 @@ static unsigned long capacity_orig_of(int cpu)
return cpu_rq(cpu)->cpu_capacity_orig;
}
+static inline bool full_capacity(int cpu)
+{
+ return (capacity_of(cpu) >= (capacity_orig_of(cpu)*768 >> 10));
+}
+
static unsigned long cpu_avg_load_per_task(int cpu)
{
struct rq *rq = cpu_rq(cpu);
@@ -5865,8 +5870,10 @@ find_idlest_cpu(struct sched_group *group, struct
task_struct *p, int this_cpu)
unsigned long load, min_load = ULONG_MAX;
unsigned int min_exit_latency = UINT_MAX;
u64 latest_idle_timestamp = 0;
+ unsigned int backup_cap = 0;
int least_loaded_cpu = this_cpu;
int shallowest_idle_cpu = -1;
+ int shallowest_idle_cpu_backup = -1;
int i;
/* Check if we have any choice: */
@@ -5876,6 +5883,7 @@ find_idlest_cpu(struct sched_group *group, struct
task_struct *p, int this_cpu)
/* Traverse only the allowed CPUs */
for_each_cpu_and(i, sched_group_span(group), &p->cpus_allowed) {
if (idle_cpu(i)) {
+ int idle_candidate = -1;
struct rq *rq = cpu_rq(i);
struct cpuidle_state *idle = idle_get_state(rq);
if (idle && idle->exit_latency < min_exit_latency) {
@@ -5886,7 +5894,7 @@ find_idlest_cpu(struct sched_group *group, struct
task_struct *p, int this_cpu)
*/
min_exit_latency = idle->exit_latency;
latest_idle_timestamp = rq->idle_stamp;
- shallowest_idle_cpu = i;
+ idle_candidate = i;
} else if ((!idle || idle->exit_latency ==
min_exit_latency) &&
rq->idle_stamp > latest_idle_timestamp) {
/*
@@ -5895,7 +5903,16 @@ find_idlest_cpu(struct sched_group *group, struct
task_struct *p, int this_cpu)
* a warmer cache.
*/
latest_idle_timestamp = rq->idle_stamp;
- shallowest_idle_cpu = i;
+ idle_candidate = i;
+ }
+
+ if (idle_candidate != -1) {
+ if (full_capacity(idle_candidate)) {
+ shallowest_idle_cpu = idle_candidate;
+ } else if (capacity_of(idle_candidate) >
backup_cap) {
+ shallowest_idle_cpu_backup =
idle_candidate;
+ backup_cap =
capacity_of(idle_candidate);
+ }
}
} else if (shallowest_idle_cpu == -1) {
load = weighted_cpuload(cpu_rq(i));
@@ -5906,7 +5923,11 @@ find_idlest_cpu(struct sched_group *group, struct
task_struct *p, int this_cpu)
}
}
- return shallowest_idle_cpu != -1 ? shallowest_idle_cpu :
least_loaded_cpu;
+ if (shallowest_idle_cpu != -1)
+ return shallowest_idle_cpu;
+
+ return (shallowest_idle_cpu_backup != -1 ?
+ shallowest_idle_cpu_backup : least_loaded_cpu);
}
#ifdef CONFIG_SCHED_SMT
--
2.7.4
