Minor nit: Patch version missing in the subject line.

Other than that: Reviewed-by: Atish Patra atish.patra@oracle.com

Regards, Atish ----- Original Message ----- From: rohit.k.jain@oracle.com To: linux-kernel@vger.kernel.org, eas-dev@lists.linaro.org Cc: peterz@infradead.org, mingo@redhat.com, joelaf@google.com, atish.patra@oracle.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, morten.rasmussen@arm.com Sent: Saturday, October 7, 2017 6:44:47 PM GMT -06:00 US/Canada Central Subject: [PATCH 1/3] sched/fair: Introduce scaled capacity awareness in find_idlest_cpu code path

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 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