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Date: Thu, 5 Jul 2012 22:33:35 +0400
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To: Johannes Weiner <hannes@cmpxchg.org>
CC: Rik van Riel <riel@redhat.com>, Andrea Arcangeli <aarcange@redhat.com>,
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Subject: Re: [PATCH 09/40] autonuma: introduce kthread_bind_node()
References: <1340888180-15355-1-git-send-email-aarcange@redhat.com> <1340888180-15355-10-git-send-email-aarcange@redhat.com> <4FEDCB7A.1060007@redhat.com> <20120629163820.GQ6676@redhat.com> <4FEDDE99.2090105@redhat.com> <20120705130902.GF7881@cmpxchg.org>
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On 07/05/2012 05:09 PM, Johannes Weiner wrote:
> In the very first review iteration of AutoNUMA, Peter argued that the
> scheduler people want to use this flag in other places where they rely
> on this thing meaning a single cpu, not a group of them (check out the
> cpumask test in debug_smp_processor_id() in lib/smp_processor_id.c).
> 
> He also argued that preventing root from rebinding the numa daemons is
> not critical to this feature at all.  And I have to agree.

Despite not being a scheduler expert, I'll have to side with that as
well. The thing I have in mind is: We have people whose usecase depend
on completely isolating cpus, with nothing but a specialized task
running on it. For those people, even the hard binding between cpu0 and
the timer interrupt is a big problem.

If you force a per-node binding of a kthread, you are basically saying
that those people are unable to isolate a node. Or else, that they have
to choose between that, and AutoNUMA. Both are suboptimal choices, to
say the least.