Re: [External] Re: [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core is found

[Hao Jia]

On 2022/10/24 Mel Gorman wrote:
> On Fri, Oct 21, 2022 at 02:15:57PM +0800, Hao Jia wrote:
> > In update_numa_stats() we try to find an idle cpu on the NUMA node,
> > preferably an idle core. When we find an idle core,
> > we can stop searching.
> >
> > Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
> > ---
> >   kernel/sched/fair.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index e4a0b8bd941c..b7cbec539c77 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1792,7 +1792,7 @@ static void update_numa_stats(struct task_numa_env *env,
> >   		ns->nr_running += rq->cfs.h_nr_running;
> >   		ns->compute_capacity += capacity_of(cpu);
> >   
> > -		if (find_idle && !rq->nr_running && idle_cpu(cpu)) {
> > +		if (find_idle && idle_core < 0 && !rq->nr_running && idle_cpu(cpu)) {
> >   			if (READ_ONCE(rq->numa_migrate_on) ||
> >   			    !cpumask_test_cpu(cpu, env->p->cpus_ptr))
> >   				continue;
> > @@ -1801,6 +1801,9 @@ static void update_numa_stats(struct task_numa_env *env,
> >   				ns->idle_cpu = cpu;
> >   
> >   			idle_core = numa_idle_core(idle_core, cpu);
> > +			/* If we find an idle core, stop searching. */
> > +			if (idle_core >= 0)
> > +				ns->idle_cpu = idle_core;
> >   		}
> >   	}
> >   	rcu_read_unlock();
> > @@ -1808,9 +1811,6 @@ static void update_numa_stats(struct task_numa_env *env,
> >   	ns->weight = cpumask_weight(cpumask_of_node(nid));
> >   
> >   	ns->node_type = numa_classify(env->imbalance_pct, ns);
> > -
> > -	if (idle_core >= 0)
> > -		ns->idle_cpu = idle_core;
> >   }
> >   
>
> Remove the change in the first hunk and call break in the second hunk
> after updating ns->idle_cpu.

Yes, thanks for your review.
If I understand correctly, some things might look like this.

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e4a0b8bd941c..dfcb620bfe50 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1792,7 +1792,7 @@ static void update_numa_stats(struct task_numa_env 
*env,
                ns->nr_running += rq->cfs.h_nr_running;
                ns->compute_capacity += capacity_of(cpu);

-               if (find_idle && !rq->nr_running && idle_cpu(cpu)) {
+               if (find_idle && idle_core < 0 && !rq->nr_running && 
idle_cpu(cpu)) {
                        if (READ_ONCE(rq->numa_migrate_on) ||
                            !cpumask_test_cpu(cpu, env->p->cpus_ptr))
                                continue;

Thanks,
Hao