Re: [RFC PATCH 07/13] sched: Add core wide task selection and scheduling.

Tim Chen
2020-04-16T23:32:32Z

On 4/14/20 6:35 AM, Peter Zijlstra wrote:
> On Wed, Mar 04, 2020 at 04:59:57PM +0000, vpillai wrote:
>> +static struct task_struct *
>> +pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>> +{
>> + struct task_struct *next, *max = NULL;
>> + const struct sched_class *class;
>> + const struct cpumask *smt_mask;
>> + int i, j, cpu;
>> + bool need_sync = false;
>
> AFAICT that assignment is superfluous. Also, you violated the inverse
> x-mas tree.
>
>> +
>> + cpu = cpu_of(rq);
>> + if (cpu_is_offline(cpu))
>> + return idle_sched_class.pick_next_task(rq);
>
> Are we actually hitting this one?
>

I did hit this race when I was testing taking cpu offline and online,
which prompted the check of cpu being offline.

Tim