Messages in this thread | | | Date | Tue, 12 Jan 2010 14:31:53 -0600 (CST) | From | Christoph Lameter <> | Subject | Re: [RFC PATCH 1/5] use nr_cpus= to set nr_cpu_ids early |
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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 ?
> 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.
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