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SubjectRe: [PATCH 11/39] autonuma: CPU follow memory algorithm
On 03/26/2012 02:25 PM, Peter Zijlstra wrote:
> On Mon, 2012-03-26 at 19:45 +0200, Andrea Arcangeli wrote:
>> @@ -3220,6 +3214,8 @@ need_resched:
>>
>> post_schedule(rq);
>>
>> + sched_autonuma_balance();
>> +
>> sched_preempt_enable_no_resched();
>> if (need_resched())
>> goto need_resched;
>
> I already told you, this isn't ever going to happen. You do _NOT_ put a
> for_each_online_cpu() loop in the middle of schedule().

Agreed, it looks O(N), but because every CPU will be calling
it its behaviour will be O(N^2) and has the potential to
completely break systems with a large number of CPUs.

Finding a lower overhead way of doing the balancing does not
seem like an unsurmountable problem.

> You also do not call stop_one_cpu(migration_cpu_stop) in schedule to
> force migrate the task you just scheduled to away from this cpu. That's
> retarded.
>
> Nacked-by: Peter Zijlstra<a.p.zijlstra@chello.nl>


--
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