Re: Re: [Xen-changelog] Create new vcpu_op() hypercall. Replaces old boot_vcpu()

[Ryan Harper <ryanh@us.ibm.com>]

* Keir Fraser <Keir.Fraser@cl.cam.ac.uk> [2005-10-03 15:56]:
> 
> On 3 Oct 2005, at 19:42, Ryan Harper wrote:
> 
> >Both do_boot_vcpu() and now VCPU_CREATE rely on domU kernel playing 
> >nice
> >and not making the hypercall more than has been indicated in the shared
> >table when we built the domain (nr_vcpus).  Wouldn't it be better to
> >have the domain creation hypercall specify the number of vcpus for a
> >domain (as well as a cpumap to indicate which physical cpus are to be
> >used) and alloc vcpu structures at that point leaving the vcpu_ops() to
> >get context and unpause the vcpu?
> >
> >If I put together a patch that mode the above change, would that be
> >considered?
> 
> I think there's not much in it -- allocating on demand vs. allocate at 
> domain build time. I think the simplest patch would be for Xen to be 
> passed a max_vcpuid or max_vcpus and apply the appropriate simple check 
> at VCPUOP_create.
> 
> I'd take a patch that adds a new dom0 op to set that value 
> (DOM0_SET_MAX_VCPUS or somesuch), applies the appropriate check inside 
> Xen. Also that plumbs that hypercall into the Python wrapper, and adds 
> a call to that command in xend (both during initial build and on 
> save/restore).

I was also thinking toward NUMA systems where I'd like to know which
physical cpus are being utilized for a given domain so when we allocate
memory for a domain we can try to localize those allocations to the cpus
that will be using it.  Currently domain memory allocation happens
before secondary processors are selected.

I'd rather see domain creation take both max_vcpus and cpu placement
bitmaps instead, but if that is not acceptable for 3.0, I'll go ahead
and work up the patch as described since it needs to be resolved for
3.0.

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com