linux-kernel - Re: [PATCH] sched/fair: Fix wrong cpu selecting from isolated domain

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Message-ID: <495238bd-ea0d-56c6-4a9c-7b18deafcc8f@linux.alibaba.com>
Date:   Tue, 25 Aug 2020 17:27:42 +0800
From:   xunlei <xlpang@...ux.alibaba.com>
To:     Jiang Biao <benbjiang@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Wetp Zhang <wetp.zy@...ux.alibaba.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Fix wrong cpu selecting from isolated domain

On 2020/8/25 下午2:37, Jiang Biao wrote:
> On Mon, 24 Aug 2020 at 20:31, Xunlei Pang <xlpang@...ux.alibaba.com> wrote:
>>
>> We've met problems that occasionally tasks with full cpumask
>> (e.g. by putting it into a cpuset or setting to full affinity)
>> were migrated to our isolated cpus in production environment.
>>
>> After some analysis, we found that it is due to the current
>> select_idle_smt() not considering the sched_domain mask.
>>
>> Fix it by checking the valid domain mask in select_idle_smt().
>>
>> Fixes: 10e2f1acd010 ("sched/core: Rewrite and improve select_idle_siblings())
>> Reported-by: Wetp Zhang <wetp.zy@...ux.alibaba.com>
>> Signed-off-by: Xunlei Pang <xlpang@...ux.alibaba.com>
>> ---
>>  kernel/sched/fair.c | 9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 1a68a05..fa942c4 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6075,7 +6075,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
>>  /*
>>   * Scan the local SMT mask for idle CPUs.
>>   */
>> -static int select_idle_smt(struct task_struct *p, int target)
>> +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
>>  {
>>         int cpu;
>>
>> @@ -6083,7 +6083,8 @@ static int select_idle_smt(struct task_struct *p, int target)
>>                 return -1;
>>
>>         for_each_cpu(cpu, cpu_smt_mask(target)) {
>> -               if (!cpumask_test_cpu(cpu, p->cpus_ptr))
>> +               if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
>> +                   !cpumask_test_cpu(cpu, sched_domain_span(sd)))
> Maybe the following change could be better, :)
> for_each_cpu_and(cpu, cpu_smt_mask(target), sched_domain_span(sd))
> keep a similar style with select_idle_core/cpu, and could reduce loops.
> 

I thought that, but given that smt mask is usually small, the original
code may run a bit faster?

> Just an option.
> Reviewed-by: Jiang Biao <benbjiang@...cent.com>
> 

Thanks :-)