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xen-devel
Re: [Xen-devel] [PATCH 2/3] xend: Add multiple cpumasks support
* Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx> [2006-08-14 17:04]:
> > Are you interested in the multi cpumask approach?
>
> Yes: it certainly doesn't hurt to have that flexibility.
>
> > If so any thoughts on how
> > you'd like to see multiple cpumasks in the config file?
>
> Either Keir's cpu[X] = "Y" approach or my cpu = [ "A","B","C" ] approach
> seem workable.
Your last email seemed to indicate to me that you didn't like using
quoted values in a list to separate per-vcpu cpumask values. Maybe I
was mistaken.
>
> Keir's approach is rather ill defined if someone tries using both cpu=
> and cpu[X]= in the same config file, but I don't see that as a big
> problem. Take your pick :-)
I'm leaning toward the list notation since I already have code that
parses that properly.
>
> BTW: does the right thing happen in the face of vcpu hot plugging? i.e.
> if I unplug a vcpu and put it back in do I keep the old mask? If I add
> vcpus what mask do they get?
unplug events only affect a vcpu's status. The internal struct
vcpu in the hypervisor is not de-allocated/re-allocated during hotplug
events.
We don't currently support a hotadd for vcpus that weren't allocated at
domain creation time. The current method for simulating hot-add would
be to start a domain with 32 VCPUS and disable all by the number of
vcpus you currently want. Ryan Grimm posted a patch back in February
that had xend do this by adding a new config option, max_vcpus, which
was used when calling xc_domain_max_vcpus() having the hypervisor alloc
that max number of vcpus and then using the vcpus parameter to determine
how many to bring online.
>
> We should probably add a 'vcpu-pin' variant that enables the mask to be
> set for all vcpus. Perhaps '-1' for the vcpu number? Or should we add
> 'vcpu-pin-all'?
vcpu-pin using -1 is probably the quickest, least intrusive method to
get this behavior. We could also use a keyword, all for instance:
xm vcpu-pin vm1 all 0-4,^5
>
> [secondly, what do you think about implicitly defaulting the mask to all
> 1's if the first item in a cpu mask is an exclusion? e.g. ^1]
That makes sense. I'll include a patch in the set to add this behavior.
--
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253 T/L: 678-9253
ryanh@xxxxxxxxxx
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