linux-kernel - Re: [git pull] cpus4096 fixes

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Message-ID: <alpine.LFD.1.10.0807271511120.3486@nehalem.linux-foundation.org>
Date:	Sun, 27 Jul 2008 15:17:14 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...IV.linux.org.uk>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Travis <travis@....com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [git pull] cpus4096 fixes

On Sun, 27 Jul 2008, Al Viro wrote:
> 
> ITYM "one 32.5kB array" -
> (u64[65][64]){[1][0] = 1, [2][0] = 2, [3][0] = 4, ..., [64][0] = 1ULL<<63}
> would work just fine.  You were saying...?

Yeah, you can optimize it even more, I agree. But even the _trivial_ one 
gets you to linear memory use (rather than something that is O(n^2) in 
number of CPU's) and makes the thing a non-issue. But yes, there's another 
almost-factor-of-two that you can get by being clever.

But in fact, I think your optimization would not just use less memory, but 
yes, it's also easier to write the initializer for (with just a couple of 
levels of macros to avoid having to do 64 entries by hand).

So yes, make it so. Please.

		Linus

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