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SubjectRe: [PATCH 2/3] sched/fair: Introduce scaled capacity awareness in select_idle_sibling code path
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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));

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