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Date: Tue, 27 Mar 2012 19:09:30 +0200
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 11/39] autonuma: CPU follow memory algorithm
Message-ID: <20120327170929.GA28771@gmail.com>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Linus Torvalds <torvalds@linux-foundation.org>, Hillf Danton <dhillf@gmail.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Dan Smith <danms@us.ibm.com>, Paul Turner <pjt@google.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Lee Schermerhorn <Lee.Schermerhorn@hp.com>, linux-mm@kvack.org, Suresh Siddha <suresh.b.siddha@intel.com>, Mike Galbraith <efault@gmx.de>, Bharata B Rao <bharata.rao@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Johannes Weiner <hannes@cmpxchg.org>, linux-kernel@vger.kernel.org


* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> You can talk pretty much anything down to O(1) that way. Take 
> an algorithm that is O(n) in the number of tasks, since you 
> know you have a pid-space constraint of 30bits you can never 
> have more than 2^30 (aka 1Gi) tasks, hence your algorithm is 
> O(2^30) aka O(1).

We can go even further than that, IIRC all physical states of 
this universe fit into a roughly 2^1000 finite state-space, so 
every computing problem in this universe is O(2^1000), i.e. 
every computing problem we can ever work on is O(1).

Really, I think Andrea is missing the big picture here.

Thanks,

	Ingo

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