linux-kernel - Re: [PATCH 12/35] autonuma: CPU follow memory algorithm

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Message-ID: <4FC4D513.7010700@redhat.com>
Date:	Tue, 29 May 2012 09:54:27 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 12/35] autonuma: CPU follow memory algorithm

On 05/29/2012 09:00 AM, Peter Zijlstra wrote:
> On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
>> @@ -3274,6 +3268,8 @@ need_resched:
>>
>>          post_schedule(rq);
>>
>> +       sched_autonuma_balance();
>> +
>>          sched_preempt_enable_no_resched();
>>          if (need_resched())
>>                  goto need_resched;
>
>
>
>> +void sched_autonuma_balance(void)
>> +{
>
>> +       for_each_online_node(nid) {
>> +       }
>
>> +       for_each_online_node(nid) {
>> +               for_each_cpu_and(cpu, cpumask_of_node(nid), allowed) {
>
>
>> +               }
>> +       }
>
>> +       stop_one_cpu(this_cpu, migration_cpu_stop,&arg);
>> +}
>
> NAK
>
> You do _NOT_ put a O(nr_cpus) or even O(nr_nodes) loop in the middle of
> schedule().
>
> I see you've made it conditional, but schedule() taking that long --
> even occasionally -- is just not cool.
>
> schedule() calling schedule() is also an absolute abomination.
>
> You were told to fix this several times..

Do you have any suggestions for how Andrea could fix this?

Pairwise comparisons with a busy CPU/node?

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