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SubjectRe: [PATCH 16/18] sched: Avoid overloading CPUs on a preferred NUMA node
On Mon, Jul 15, 2013 at 04:20:18PM +0100, Mel Gorman wrote:
> ---
> kernel/sched/fair.c | 105 +++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 83 insertions(+), 22 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3f0519c..8ee1c8e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -846,29 +846,92 @@ static inline int task_faults_idx(int nid, int priv)
> return 2 * nid + priv;
> }
>
> -static unsigned long weighted_cpuload(const int cpu);
> +static unsigned long source_load(int cpu, int type);
> +static unsigned long target_load(int cpu, int type);
> +static unsigned long power_of(int cpu);
> +static long effective_load(struct task_group *tg, int cpu, long wl, long wg);
> +
> +static int task_numa_find_cpu(struct task_struct *p, int nid)
> +{
> + int node_cpu = cpumask_first(cpumask_of_node(nid));
> + int cpu, src_cpu = task_cpu(p), dst_cpu = src_cpu;
> + unsigned long src_load, dst_load;
> + unsigned long min_load = ULONG_MAX;
> + struct task_group *tg = task_group(p);
> + s64 src_eff_load, dst_eff_load;
> + struct sched_domain *sd;
> + unsigned long weight;
> + bool balanced;
> + int imbalance_pct, idx = -1;
>
> + /* No harm being optimistic */
> + if (idle_cpu(node_cpu))
> + return node_cpu;
>
> + /*
> + * Find the lowest common scheduling domain covering the nodes of both
> + * the CPU the task is currently running on and the target NUMA node.
> + */
> + rcu_read_lock();
> + for_each_domain(src_cpu, sd) {
> + if (cpumask_test_cpu(node_cpu, sched_domain_span(sd))) {
> + /*
> + * busy_idx is used for the load decision as it is the
> + * same index used by the regular load balancer for an
> + * active cpu.
> + */
> + idx = sd->busy_idx;
> + imbalance_pct = sd->imbalance_pct;
> + break;
> + }
> + }
> + rcu_read_unlock();
>
> + if (WARN_ON_ONCE(idx == -1))
> + return src_cpu;
>
> + /*
> + * XXX the below is mostly nicked from wake_affine(); we should
> + * see about sharing a bit if at all possible; also it might want
> + * some per entity weight love.
> + */
> + weight = p->se.load.weight;
>
> + src_load = source_load(src_cpu, idx);
> +
> + src_eff_load = 100 + (imbalance_pct - 100) / 2;
> + src_eff_load *= power_of(src_cpu);
> + src_eff_load *= src_load + effective_load(tg, src_cpu, -weight, -weight);

So did you try with this effective_load() term 'missing'?

> +
> + for_each_cpu(cpu, cpumask_of_node(nid)) {
> + dst_load = target_load(cpu, idx);
> +
> + /* If the CPU is idle, use it */
> + if (!dst_load)
> + return dst_cpu;
> +
> + /* Otherwise check the target CPU load */
> + dst_eff_load = 100;
> + dst_eff_load *= power_of(cpu);
> + dst_eff_load *= dst_load + effective_load(tg, cpu, weight, weight);
> +
> + /*
> + * Destination is considered balanced if the destination CPU is
> + * less loaded than the source CPU. Unfortunately there is a
> + * risk that a task running on a lightly loaded CPU will not
> + * migrate to its preferred node due to load imbalances.
> + */
> + balanced = (dst_eff_load <= src_eff_load);
> + if (!balanced)
> + continue;
> +
> + if (dst_load < min_load) {
> + min_load = dst_load;
> + dst_cpu = cpu;
> }
> }
>
> + return dst_cpu;
> }


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