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SubjectRe: [PATCH 16/18] sched: Avoid overloading CPUs on a preferred NUMA node
On Mon, Jul 15, 2013 at 10:03:21PM +0200, Peter Zijlstra wrote:
> 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'?
>

Yes, it performed worse in tests. Looking at it, I figured that it would
have to perform worse unless effective_load regularly returns negative
values.

--
Mel Gorman
SUSE Labs


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