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Message-ID: <20080826192848.GA20653@redhat.com>
Date: Tue, 26 Aug 2008 15:28:48 -0400
From: Dave Jones <davej@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Travis <travis@....com>,
"Alan D. Brunelle" <Alan.Brunelle@...com>,
Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Kernel Testers List <kernel-testers@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Arjan van de Ven <arjan@...ux.intel.com>,
Rusty Russell <rusty@...tcorp.com.au>,
"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
"Luck, Tony" <tony.luck@...el.com>, Jack Steiner <steiner@....com>,
Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c -
bisected
On Tue, Aug 26, 2008 at 12:09:46PM -0700, Linus Torvalds wrote:
> If you want the default kernel to support 4k cores, we'll need to fix the
> stack usage. I don't think that is impossible, but IT IS NOT GOING TO
> HAPPEN for 2.6.27.
>
> And quite frankly, if some vendor like RedHat enables NR_CPUS=4096 by
> default, they are totally and utterly crazy.
heh. *picks through Fedora changelog*
* Thu Aug 14 2008 Dave Jones <davej@...hat.com>
- Bump max cpus supported on x86-64 to 4096. Just to see what happens.
I never did get to find out unfortunatly, because of the security fiasco
in Fedora infrastructure the last week or two.
> But some SGI-specific binary that is meant for SGI machines only, and has
> been extensively tested with the setup used on SGI machines is a different
> thing.
Every extra kernel image a distro vendor ends up shipping has an associated cost.
* build time: It currently takes about 2 hours for a set of Fedora RPMs.
For RHEL it'll be even worse due to the extra archs).
Killing off -smp specific builds was a big win for us in this regard.
Adding extra flavours is always painful.
* diskspace (distro kernels aren't small. With the associated debugging symbols,
they take up a shitload of disk space really fast).
* Having everyone running the same kernel makes it much easier to test/debug.
Our QA guys hate adding extra columns to their test matrix.
But yes, for this to be even remotely feasible, there has to be a negligable
performance cost associated with it, which right now, we clearly don't have.
Given that the number of people running 4096 CPU boxes even in a few years time
will still be tiny, punishing the common case is obviously absurd.
Dave
--
http://www.codemonkey.org.uk
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