Re: [PATCH v2 2/3] sched/fair: Ignore isolated cpus in update_numa_stat

[Chuyi Zhou]

Hello Waiman,

在 2025/1/8 02:39, Waiman Long 写道:
> On 1/3/25 1:59 AM, Chuyi Zhou wrote:
> > Now update_numa_stats() iterates each cpu in a node to gather load
> > information for the node and attempts to find the idle cpu as a candidate
> > best_cpu within the node.
> >
> > In update_numa_stats() we should take into account the scheduling domain.
> > This is because the "isolcpus" kernel command line option and cpuset iso-
> > late partitions can remove CPUs from load balance. Similar to task wakeup
> > and periodic load balancing, we should not involve isolated CPUs in NUMA
> > balancing. When gathering load information for nodes, we need to 
> > ignore the
> > load of isolated CPUs. This change also avoids selecting an isolated CPU
> > as the idle_cpu.
> >
> > Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
> > ---
> >   kernel/sched/fair.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index f544012b9320..a0139659fe7a 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -2125,6 +2125,11 @@ static void update_numa_stats(struct 
> > task_numa_env *env,
> >       for_each_cpu(cpu, cpumask_of_node(nid)) {
> >           struct rq *rq = cpu_rq(cpu);
> > +        /* skip isolated cpus' load */
> > +        if (!rcu_dereference(rq->sd))
> > +            continue;
> > +
> > +        ns->weight++;
> >           ns->load += cpu_load(rq);
> >           ns->runnable += cpu_runnable(rq);
> >           ns->util += cpu_util_cfs(cpu);
> > @@ -2144,8 +2149,6 @@ static void update_numa_stats(struct 
> > task_numa_env *env,
> >       }
> >       rcu_read_unlock();
> > -    ns->weight = cpumask_weight(cpumask_of_node(nid));
> > -
> >       ns->node_type = numa_classify(env->imbalance_pct, ns);
> >       if (idle_core >= 0)
>
> You should initalize ns->weight to 0 first before iteration to prevent 
> pre-existing ns->weight value from corrupting the result.
>
> Cheers,
> Longman

Thanks for your review.

We have already memset ns to 0 before the start of update_numa_stats(), 
so I think it should be okay here.