Re: [Xen-devel] RE: [PATCH] Allocate vmcs pages when system booting

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 15/01/2010 09:30, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>>>> "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> 15.01.10 10:06 >>>
>> b) Can we still turn to the original patch, i.e. pre-allocate all VMCS pages
>> for all possible CPU?
> 
> I'm generally opposed to pre-allocations, at least as long as all CPUs are
> considered 'possible'. Building with a relatively high nr_cpus= setting
> and then running on a relatively small system results in (close to)
> unacceptable overhead.
> 
> In fact it's really not clear to me why cpu_possible_map must be set to
> CPU_MASK_ALL - if Linux has ways to avoid this, Xen should have too.

Does Linux manage a good reliable job of cutting down cpu_possible_map? That
would save cpu_possible_map in my eyes, if we could do that. Otherwise it is
indeed pretty useless now. Either way, I'd like cpu hotplug notifier chains
in the 4.1 development window.

 -- Keir



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