Re: [PATCH v3 ]libxl: allow to set more than 31 vcpus

[Dario Faggioli <raistlin@linux.it>]

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On Fri, 2012-06-01 at 11:38 +0100, Ian Campbell wrote: 
> > Anyway, I just tried 25 and 33 and 65, and creation of the domain worked
> > without raising any errors! Then I double-checked, and saw that, in the
> > 'above 16' cases, Xen deliberately paused a lot of VCPUs. Also, if I log
> > into the guest /proc/cpuinfo reports only CPUs 0 and 32 (and 64 in the
> > 65 VCPUs case).
> 
> All 64 online?
> 
I see all of them from the host (xl vcpu-list) but a kind of random
number of them from the guest...

> It might be that the issue being fixed here only manifests on HVM. I'm
> not really sure how 64 would work otherwise since cur_vcpus in the IDL
> is definitely an int, which is what needs fixing!
> 
and in fact, I agreed with that part of the patch. Also, yes, I'm trying
PV but can try HVM as well and see what happens.

> libxl__build_post is also probably buggy with max_vcpus >
> nr-bits-in(curr_vcpus) and from the looks of it it just overflows off
> the end(!), which is also fixed here...
> 
What I can do is trying again with the patch applied, and if it still
behaves weird I'll go seeing what might be still missing.

> > "max. number of cpus supported by hypervisor" to be different from the
> > actual number of physical processors, and I was sort-of mislead by the
> > machine I use to test Xen every day (where that is actually happening!).
> > If it is not like that, I guess I can agree with you on this change.
> 
> It's certainly supposed to be "get max. number of physical cpus", quite
> how that relates to the actual number of physical cpus I'm not sure.
> 
> It's definitely not something to do with virtual cpus (for which there
> is a limit, but not this one...)
> 
Ok, with that "physical" you're putting there, I see and agree it could
be useful untie it from the "virtual world". :-)

Thanks and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)



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