Messages in this thread | | | Date | Thu, 2 Oct 2008 16:09:07 -0400 | From | Chuck Ebbert <> | Subject | Re: [patch x86/core] x86: allow number of additional hotplug CPUs to be set at compile time |
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On Thu, 2 Oct 2008 21:44:09 +0200 Andi Kleen <andi@firstfloor.org> wrote:
> On Thu, Oct 02, 2008 at 03:25:21PM -0400, Chuck Ebbert wrote: > > On Thu, 02 Oct 2008 11:12:51 +0200 > > Andi Kleen <andi@firstfloor.org> wrote: > > > > > Chuck Ebbert <cebbert@redhat.com> writes: > > > > > > > The default number of additional CPU IDs for hotplugging is determined > > > > by asking ACPI or mptables how many "disabled" CPUs there are in the > > > > system, but many systems get this wrong so that e.g. a uniprocessor > > > > machine gets an extra CPU allocated and never switches to single CPU > > > > mode. > > What do you mean with single cpu mode? > > e.g. the lock prefix rewriting is only determined by online CPUs, > not possible CPUs. And this only affects the possible ones. >
The prefix rewriting doesn't happen unless I boot with additional_cpus=0, maxcpus=1, or with this patch applied and the config option set. I think the rules for when/if the rewriting happens changed a while ago to avoid multiple switches and now it's not happening at all on this machine by default.
Oh, and with NR_CPUS=512 I am seeing 1.6MB per-cpu data (I'll have to check that, but I remember being surprised at how big the number was.)
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