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Subject: Re: [PATCH 12/35] autonuma: CPU follow memory algorithm
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Tue, 29 May 2012 15:00:53 +0200
In-Reply-To: <1337965359-29725-13-git-send-email-aarcange@redhat.com>
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To: Andrea Arcangeli <aarcange@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hillf Danton <dhillf@gmail.com>, Dan Smith <danms@us.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, Paul Turner <pjt@google.com>, Suresh Siddha <suresh.b.siddha@intel.com>, Mike Galbraith <efault@gmx.de>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, Bharata B Rao <bharata.rao@gmail.com>, Lee Schermerhorn <Lee.Schermerhorn@hp.com>, Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>, Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>, Christoph Lameter <cl@linux.com>

On Fri, 2012-05-25 at 19:02 +0200, Andrea Arcangeli wrote:
> @@ -3274,6 +3268,8 @@ need_resched:
> =20
>         post_schedule(rq);
> =20
> +       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);
> +}=20

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..

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