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.jain@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 c95880e..f66ac8c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5298,6 +5298,11 @@ static unsigned long cpu_avg_load_per_task(int cpu) return 0; }
+static inline bool full_capacity(int cpu) +{ + return (capacity_of(cpu) >= (capacity_orig_of(cpu)*819 >> 10)); +} + static void record_wakee(struct task_struct *p) { /* @@ -5516,9 +5521,11 @@ 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; + unsigned int backup_cap = 0; u64 latest_idle_timestamp = 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: */ @@ -5538,7 +5545,12 @@ 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; + if (full_capacity(i)) { + shallowest_idle_cpu = i; + } else if (capacity_of(i) > backup_cap) { + shallowest_idle_cpu_backup = i; + backup_cap = capacity_of(i); + } } else if ((!idle || idle->exit_latency == min_exit_latency) && rq->idle_stamp > latest_idle_timestamp) { /* @@ -5547,7 +5559,12 @@ 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; + if (full_capacity(i)) { + shallowest_idle_cpu = i; + } else if (capacity_of(i) > backup_cap) { + shallowest_idle_cpu_backup = i; + backup_cap = capacity_of(i); + } } } else if (shallowest_idle_cpu == -1) { load = weighted_cpuload(i); @@ -5558,7 +5575,11 @@ 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