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Date: Sun, 24 May 2009 21:52:45 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Yinghai Lu <yinghai@kernel.org>, Pekka J Enberg <penberg@cs.helsinki.fi>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Jeff Garzik <jgarzik@pobox.com>, Alexander Viro <viro@ftp.linux.org.uk>,
       Rusty Russell <rusty@rustcorp.com.au>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [GIT PULL] scheduler fixes
References: <alpine.LFD.2.01.0905180850110.3301@localhost.localdomain> <20090518164921.GA6903@elte.hu> <alpine.LFD.2.01.0905180955550.3301@localhost.localdomain> <20090518170909.GA1623@elte.hu> <20090518190320.GA20260@elte.hu> <alpine.LFD.2.01.0905181208130.3301@localhost.localdomain> <20090518202031.GA26549@elte.hu> <alpine.LFD.2.01.0905181457320.3301@localhost.localdomain> <Pine.LNX.4.64.0905241911120.12189@melkki.cs.Helsinki.FI> <4A199327.5030503@kernel.org> <20090525025353.GA2580@elte.hu>
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Ingo Molnar wrote:
> 
> Would it be possible to restructure things to move kmalloc init to 
> before IRQ init as well? We have a couple of uglinesses there too.
> 
> Conceptually, memory should be the first thing set up in general, in 
> a kernel. It does not need IRQs, timers, the scheduler or any of the 
> IO facilities and abstractions. All of them need memory though - and 
> as Linux scales to more and more hardware via the same single image, 
> so will we get more and more dynamic concepts like cpumask_var_t and 
> sparse-irqs, which want to allocate very early.
> 
> setup_arch() is one huge function that sets up all architecture 
> details at once - but if we split a separate setup_arch_mem() out of 
> it, and left the rest in setup_arch (and moved it further down), we 
> could remove much of bootmem (especially the ugly uses).
> 
> This might even be doable realistically, and we could thus librarize 
> bootmem and eliminate it from x86 at least. Perhaps.
> 

The only thing that might make sense to set up before memory might be
exceptions (as opposed to interrupts), but both of those should be
doable very very early.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.