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

[Waiman Long <llong@redhat.com>]

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@bytedance.com>
> ---
>   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