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RE: [Xen-devel] [PATCH][RESUBMIT] don't schedule unplugged vcpus

To: "Ryan Harper" <ryanh@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH][RESUBMIT] don't schedule unplugged vcpus
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Wed, 8 Jun 2005 22:42:52 +0100
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Thread-topic: [Xen-devel] [PATCH][RESUBMIT] don't schedule unplugged vcpus
> I've added in changes to DOM0_GETDOMINFO and 
> DOM0_GETVCPUCONTEXT hypercalls.  dominfo now creates a 
> vcpu_online_map bitmap which marks whether vcpus are up or 
> down.  I didn't want to clobber either the total number of 
> vcpus allocated to a domain (n_vcpu) nor the vcpu_to_cpu 
> mapping since both are still valid whether the vcpu is being 
> scheduled or not.

I don't see why we care about vcpus that are down. From the user's point
of view they've gone for good -- it just happens that Xen hasn't freed
the memory in anticipation of it being used again. What do you think?

I'd be inclined just to enter '-1' in the vcpu_to_cpu map. BTW: we could
make it an s16 rather than s32 at the same time. I think 32,768 CPUs
should keep be enough for anyone :-) 

> I modified vcpucontext to give the context for the first vcpu 
> not down.
> If the requested vcpu is down, it will return the context of 
> the next vcpu that is up, or -ESRCH if no vcpu past the 
> requested vcpu is valid.
> I modified xm list -v to display an ONLINE column which 
> indicates the online status of each vcpu in a domain.

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