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DateWed, 6 Feb 2008 21:58:05 -0800
FromAndrew Morton <>
SubjectRe: [git pull] CPU isolation extensions
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On Wed, 06 Feb 2008 21:32:55 -0800 Max Krasnyansky <maxk@qualcomm.com> wrote:
Linus, please pull CPU isolation extensions from

git://git.kernel.org/pub/scm/linux/kernel/git/maxk/cpuisol-2.6.git for-linus

The feature as a whole seems useful, and I don't actually oppose the merge based on what I see here. As long as you're really sure that cpusets are inappropriate (and bear in mind that Paul has a track record of being wrong on this :)). But I see a few glitches


- There are two separate and identical implementations of cpu_unusable(cpu). Please do it once, in a header, preferably with C function, not macros.

- The Kconfig help is a bit scraggly:

+config CPUISOL_STOPMACHINE
+ bool "Do not halt isolated CPUs with Stop Machine (HIGHLY EXPERIMENTAL)" + depends on CPUISOL && STOP_MACHINE && EXPERIMENTAL + help
+ If this option is enabled kernel will not halt isolated CPUs when Stop Machine
"the kernel"

text is too wide

+ is triggered.
+ Stop Machine is currently only used by the module insertion and removal logic. + Please note that at this point this feature is highly experimental and maybe + dangerous. It is not known to really brake anything but can potentially + introduce an instability.

s/maybe/may be/
s/brake/break/


Neither this text, nor the changelog nor the code comments tell us what the potential instability with stopmachine *is*? Or maybe I missed it.
- Adding new sysfs files without updating Documentation/ABI/ makes Greg cry.

- Why is cpu_isolated_map exported to modules? Just for api consistency, it appears?


pre-existing problems:

- isolated_cpu_setup() has an on-stack array of NR_CPUS integers. This will consume 4k of stack on ia64 (at least). We'll just squeak through for a ittle while, but this needs to be fixed. Just move it into __initdata.

- isolated_cpu_setup() expects that the user can provide an up-to-1024 character kernel boot parameter. Is this reasonable given cpu command line limits, and given that NR_CPUS will surely grow beyond 1024 in the future?





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