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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 15.01.10 11:31 >>>
>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.

Only now got to look into this: Linux simply counts the disabled CPUs
along with the present ones, plus it allows a command line override to
the number of CPU slots reserved for hotplug. I just put together
something similar, partly copying code over from there. Will submit
post-4.0.

Jan


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