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Message-ID: <20081216211848.GO14787@elte.hu>
Date: Tue, 16 Dec 2008 22:18:48 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Yinghai Lu <yinghai@...nel.org>
Cc: Andi Kleen <andi@...stfloor.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] add command line init_start_cpus
* Yinghai Lu <yinghai@...nel.org> wrote:
> On Sun, Dec 14, 2008 at 4:11 PM, Andi Kleen <andi@...stfloor.org> wrote:
> > Yinghai Lu <yinghai@...nel.org> writes:
> >
> >> Impact: new command line
> >>
> >> so could select cpus to be started during init stage
> >
> > maxcpus=N should do this already, at least for the first N cpus.
> > If you really need a non continuous range of N (why?) then it would
> > be better to fix maxcpus instead of adding a new option.
>
> it seems it is hard to make maxcpus= to support random cpus selecting
> and maxcpus=0 looks insane
yes, maxcpus=0 looks sucky. If we want this via a boot option then it
should be a separate one.
> also maxcpus=1, will disable smp, can you enable other cpus later in
> user space?
only booting maxcpus=0 or nosmp will disable SMP permanently. maxcpus=1
should give the boot CPU [if not then we need to fix it], and you can then
enable an arbitrary permutation of good CPUs via:
echo 1 > /sys/devices/system/cpu/cpuX/online
as long as you CONFIG_HOTPLUG_CPU enabled.
What _might_ make sense is to introduce badcpus=2,4,6 that would
permanently disnumerate all the broken CPUs, by striking that mask from
the possible-cpus-map - inaccessible to hotplugging as well. (Note that by
naming it in the inverse way the thing gets a whole new quality - the boot
option in itself explains its purpose.)
Ingo
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