Messages in this thread |  | | | Date | Tue, 12 Jan 2010 14:20:22 -0800 | | Subject | Re: [RFC PATCH 1/5] use nr_cpus= to set nr_cpu_ids early | | From | Yinghai Lu <> |
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On Tue, Jan 12, 2010 at 12:31 PM, Christoph Lameter <cl@linux-foundation.org> wrote: > On Tue, 12 Jan 2010, Yinghai Lu wrote: > >> > Why do we need this twice? >> >> maxcpus only change setup_max_cpus., and if you are using maxcpus=1, >> and you have 8 cpus installed, you can put other >> cpus back online via /sys/interface. > > Hmmm.. Strange semantics since maxcpus=0 disables smp completely. No cpu > can be activated later. Similar to nr_cpus ?
no for SMP kernel, when nr_cpus=1 is specified, it looks like only one cpu is installed physically. smp is still enabled.
maxcpus=0 is really caused misunderstanding.
other maxcpus=1 and other should be rename to boot_online_cpus=
> >> nr_cpus= is hard limit nr_cpu_ids, so if you have 16 cpus installed, >> nr_cpus=8 will make your nr_cpu_ids=8, and you can not put back >> other 8 back. and apic mode could stay with logical flat. >> this is used to simulate some debug case. for example you have kernel >> support physflat, and flat, with CONFIG_NR_CPUS=255. to run that on >> system that only have 8 cpus, you will have apic mode in logical flat. >> but if you have run the kernel on system with 32 cpus installed, it >> will switch to physflat even you have maxcpus=8 appedded. > > Ok makes sense.
good.
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