linux-kernel - Re: [GIT PULL] scheduler fixes

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Message-ID: <84144f020905241213g365362bi130669aff2be58a9@mail.gmail.com>
Date:	Sun, 24 May 2009 22:13:58 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	Alexander Viro <viro@....linux.org.uk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Matt Mackall <mpm@...enic.com>
Subject: Re: [GIT PULL] scheduler fixes

Hi Linus,

On Sun, 24 May 2009, Pekka J Enberg wrote:
>> Ingo, here's a patch that boots UMA+SMP+SLUB x86-64 kernel on qemu all
>> the way to userspace. It probably breaks bunch of things for now but
>> something for you to play with if you want.

On Sun, May 24, 2009 at 9:18 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> In fact, it would be nice to perhaps try to move it even earlier. Now you
> moved it to before the scheduler init (good!), but I do wonder if it could
> be moved up to even before the setup_per_cpu_areas() etc crud.

Oh, sure, we can look into that. I just wanted to take the
conservative approach because I worry about breaking bunch of
configurations I cannot test. I suspect it's going to get pretty hairy
if we do kmem_cache_init() even earlier. Furthermore, SLUB does sysfs
setup in kmem_cache_init() so we probably need to split slab
initialization in two stages.

On Sun, May 24, 2009 at 9:18 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> I realize that the allocator wants to use the per-CPU area, but if we have
> just the boot CPU area set up statically at that point, since it's only
> the boot CPU running, maybe we could do those per-cpu area allocations
> without the bootmem allocator too?

We probably can. I don't see any fundamental reason why slab
allocators can't bootstrap early in the boot sequence after we've set
up the page allocator.

On Sun, May 24, 2009 at 9:18 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> But even just getting bootmem out of the scheduler setup is a big
> improvement, I think. So this patch looks very promising as is.
>
> Did you test whether the other allocators were ok with this too?

SLUB and SLOB are fine but SLAB explodes. I didn't investigate it yet
but it's probably because SLAB expects interrupts to be enabled when
kmem_cache_init() is called.

                       Pekka
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