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

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Message-ID: <ced7c05a-121b-a77d-0c57-3e60abaecacd@bytedance.com>
Date:   Tue, 25 Oct 2022 11:16:29 +0800
From:   Hao Jia <jiahao.os@...edance.com>
To:     Mel Gorman <mgorman@...e.de>
Cc:     mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH 1/2] sched/numa: Stop an exhastive search
 if an idle core is found



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@...edance.com>
>> ---
>>   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