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

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Message-Id: <200807282321.53892.rusty@rustcorp.com.au>
Date:	Mon, 28 Jul 2008 23:21:53 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Travis <travis@....com>
Subject: Re: [git pull] cpus4096 fixes

On Monday 28 July 2008 18:16:39 Ingo Molnar wrote:
> * Rusty Russell <rusty@...tcorp.com.au> wrote:
> > Mike: I now think the right long-term answer is Linus' dense cpumap
> > idea + a convenience allocator for cpumasks.  We sweep the kernel for
> > all on-stack vars and replace them with one or the other.  Thoughts?
>
> The dense cpumap for constant cpumasks is OK as it's clever, compact and
> static.
>
> All-dynamic allocator for on-stack cpumasks ... is a less obvious
> choice.

Sorry, I was unclear.  "long-term" == "more than 4096 CPUs", since I thought 
that was Mike's aim.  If we only want to hack up 4k CPUS and stop, then I 
understand the current approach.

If we want huge cpu numbers, I think cpumask_alloc/free gives the clearest 
code.  So our approach is backwards: let's do that *then* put ugly hacks in 
if it's really too slow.

Cheers,
Rusty.
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