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SubjectRe: [PATCH 4/4] numa: introduce numa cling feature
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On 2019/7/11 下午10:27, Peter Zijlstra wrote:
[snip]
>> Thus we introduce the numa cling, which try to prevent tasks leaving
>> the preferred node on wakeup fast path.
>
>
>> @@ -6195,6 +6447,13 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>> if ((unsigned)i < nr_cpumask_bits)
>> return i;
>>
>> + /*
>> + * Failed to find an idle cpu, wake affine may want to pull but
>> + * try stay on prev-cpu when the task cling to it.
>> + */
>> + if (task_numa_cling(p, cpu_to_node(prev), cpu_to_node(target)))
>> + return prev;
>> +
>> return target;
>> }
>
> Select idle sibling should never cross node boundaries and is thus the
> entirely wrong place to fix anything.

Hmm.. in our early testing the printk show both select_task_rq_fair() and
task_numa_find_cpu() will call select_idle_sibling with prev and target on
different node, thus we pick this point to save few lines.

But if the semantics of select_idle_sibling() is to return cpu on the same
node of target, what about move the logical after select_idle_sibling() for
the two callers?

Regards,
Michael Wang

>

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