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

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Message-ID: <20080727210547.GC28946@ZenIV.linux.org.uk>
Date:	Sun, 27 Jul 2008 22:05:47 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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, Jul 27, 2008 at 01:15:26PM -0700, Linus Torvalds wrote:

> So when you have 4k CPU's, instead of having 4k arrays (of 4k bits each, 
> with one bit set in each array - 2MB memory total), you have exactly 64 
> arrays instead, each 8k bits in size (64kB total). 

> And once you're not being a total idiot about wasting memory that is just 
> filled with a single bit in various different places, you don't need all 
> those games to re-create the arrays in some dense format, because they're 
> already going to be dense enough. If you compile a kernel for up to 4k 
> CPU's, "wasting" that 64kB of memory is a non-issue (especially since by 
> doing this "overlapping" trick you probbaly get better cache behaviour 
> anyway).
> 
> Ok, so now that I've insulted you and your pets (they're ugly!), show me 
> wrong, and then call me a d*ckhead. ("Linus - you're a d*ckhead, and you 
> didn't understand the problem, so you're a _stupid_ d*ckhead. And my 
> pet may be ugly, but yours _smells_ bad!").
> 
> Or say "Uh, yeah, we're morons, and here's the much better patch, and we 
> won't do that again".

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...?

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