* subhra mazumdar <subhra.mazum...@oracle.com> [2019-06-26 18:29:15]:
> Rotate the cpu search window for better spread of threads. This will ensure
> an idle cpu will quickly be found if one exists.
While rotating the cpu search window is good, not sure if this can find a
idle cpu quickly. The probability of finding an idle cpu still should remain
the same. No?
>
> Signed-off-by: subhra mazumdar <subhra.mazum...@oracle.com>
> ---
> kernel/sched/fair.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> @@ -6219,9 +6219,15 @@ static int select_idle_cpu(struct task_struct *p,
> struct sched_domain *sd, int t
> }
> }
>
> + 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;
Shouldn't this assignment be outside the for loop.
With the current code,
1. We keep reassigning multiple times.
2. The last assignment happes for idle_cpu and sometimes the
assignment is for non-idle cpu.
> if (!--nr)
> return -1;
> if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
> --
> 2.9.3
>
--
Thanks and Regards
Srikar Dronamraju
