linux-kernel - Re: [PATCH 11/39] autonuma: CPU follow memory algorithm

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


* Peter Zijlstra <a.p.zijlstra@...llo.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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