linux-kernel - Re: [PATCH v2 2/3] sched/fair: Ignore isolated cpus in update_numa

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Message-ID: <0b001d74-5e4b-4dcc-86f1-55c67b1def33@bytedance.com>
Date: Wed, 8 Jan 2025 18:47:49 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: Waiman Long <llong@...hat.com>, mingo@...hat.com, peterz@...radead.org,
 juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, riel@...riel.com
Cc: chengming.zhou@...ux.dev, kprateek.nayak@....com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] sched/fair: Ignore isolated cpus in
 update_numa_stat

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@...edance.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
> 

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.