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SubjectRe: [RFC PATCH 9/9] sched: rotate the cpu search window for better spread
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On 8/30/19 11:19 PM, subhra mazumdar wrote:
> Rotate the cpu search window for better spread of threads. This will ensure
> an idle cpu will quickly be found if one exists.
>
> Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com>
> ---
> kernel/sched/fair.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 94dd4a32..7419b47 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6188,7 +6188,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> u64 avg_cost, avg_idle;
> u64 time, cost;
> s64 delta;
> - int cpu, floor, nr = INT_MAX;
> + int cpu, floor, target_tmp, nr = INT_MAX;
>
> this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
> if (!this_sd)
> @@ -6213,9 +6213,15 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> nr = floor;
> }
>
> + if (per_cpu(next_cpu, target) != -1)
> + target_tmp = per_cpu(next_cpu, target);
> + else
> + target_tmp = target;
> +
> time = local_clock();
>
> - for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
> + for_each_cpu_wrap(cpu, sched_domain_span(sd), target_tmp) {
> + per_cpu(next_cpu, target) = cpu;

Is it possible that two simultaneous select_idle_cpu call have the same target value?

> if (!--nr)
> return -1;
> if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
>

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