Re: [Eas-dev] [PATCH 2/3] sched/fair: Introduce scaled capacity awareness in select_idle_sibling code path

Minor nit: version number missing

On 10/07/2017 06:48 PM, Rohit Jain wrote:

While looking for CPUs to place running tasks on, the scheduler completely ignores the capacity stolen away by RT/IRQ tasks. This patch changes that behavior to also take the scaled capacity into account.

Signed-off-by: Rohit Jain rohit.k.jain@oracle.com

kernel/sched/fair.c | 37 ++++++++++++++++++++++++++++--------- 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index eaede50..5b1f7b9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6004,7 +6004,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int

for_each_cpu(cpu, cpu_smt_mask(core)) {
	cpumask_clear_cpu(cpu, cpus);

• 	if (!idle_cpu(cpu))
  

• 	if (!idle_cpu(cpu) || !full_capacity(cpu))
  

Do we need to skip the entire core just because 1st cpu in the core doesn't have full capacity ? Let's say that is the only idle core available. It will go and try to select_idle_cpu() to find the idlest cpu. Is it worth spending extra time to search an idle cpu with full capacity when there are idle cores available ?

Regards, Atish

		idle = false;
}

@@ -6025,7 +6025,8 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int */ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) {

• int cpu;

• int cpu, backup_cpu = -1;

• unsigned int backup_cap = 0;

  if (!static_branch_likely(&sched_smt_present)) return -1;

@@ -6033,11 +6034,17 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t for_each_cpu(cpu, cpu_smt_mask(target)) { if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) continue;

• if (idle_cpu(cpu))
  

• 	return cpu;
  

• if (idle_cpu(cpu)) {
  

• 	if (full_capacity(cpu))
  

• 		return cpu;
  

• 	if (capacity_of(cpu) > backup_cap) {
  

• 		backup_cap = capacity_of(cpu);
  

• 		backup_cpu = cpu;
  

• 	}
  

• }
  

  }

• return -1;

• return backup_cpu; }

  #else /* CONFIG_SCHED_SMT */

@@ -6066,6 +6073,8 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t u64 time, cost; s64 delta; int cpu, nr = INT_MAX;

• int backup_cpu = -1;

• unsigned int backup_cap = 0;

  this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc)); if (!this_sd)

@@ -6096,10 +6105,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t return -1; if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) continue;

• if (idle_cpu(cpu))
  

• 	break;
  

• if (idle_cpu(cpu)) {
  

• 	if (full_capacity(cpu)) {
  

• 		backup_cpu = -1;
  

• 		break;
  

• 	} else if (capacity_of(cpu) > backup_cap) {
  

• 		backup_cap = capacity_of(cpu);
  

• 		backup_cpu = cpu;
  

• 	}
  

• }
  

  }

• if (backup_cpu >= 0)

• cpu = backup_cpu;
  

  time = local_clock() - time; cost = this_sd->avg_scan_cost; delta = (s64)(time - cost) / 8;

@@ -6116,13 +6134,14 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) struct sched_domain *sd; int i;

• if (idle_cpu(target))

• if (idle_cpu(target) && full_capacity(target)) return target;

  /*

  • If the previous cpu is cache affine and idle, don't be stupid.

  */

• if (prev != target && cpus_share_cache(prev, target) && idle_cpu(prev))

• if (prev != target && cpus_share_cache(prev, target) && idle_cpu(prev)

•    && full_capacity(prev))
  

  return prev;

  sd = rcu_dereference(per_cpu(sd_llc, target));