Re: [Xen-devel] [RFC] Extending numbers of event channels

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.12.12 at 19:09, Wei Liu <Wei.Liu2@xxxxxxxxxx> wrote:
> On Mon, 2012-12-03 at 18:00 +0000, Jan Beulich wrote:
>> >>> On 03.12.12 at 18:52, Wei Liu <Wei.Liu2@xxxxxxxxxx> wrote:
>> > On Mon, 2012-12-03 at 17:35 +0000, Jan Beulich wrote:
>> >> Doesn't the guest also need to set up space for the 2nd level?
>> >> 
>> > 
>> > Yes. That will be embedded in percpu struct vcpu_info, which will be
>> > also register via the same hypercall op.
>> 
>> "struct vcpu_info"? Same hypercall? Or are you mixing up types?
>> 
> 
> What I meant was the second level will be embedded in struct vcpu_info,
> and the 2nd level will be registered via some hypercall (not the struct
> vcpu_info).

I would strongly recommend against embedding in
struct vcpu_info, particularly in the context of intending to
allow for having further levels in the future.

Plus I don't think you really can embed this - there's just not
enough space left (I'm sure you're aware that you can't
extend the structure in size), in fact there's no space left at
all in the architecture independent part of the structure.

The only option you have is to declare the array you need to
add to immediately follow the structure when having used
the placement hypercall. That would probably be acceptable
for the second from the top level, but you'd again run into
(space) issues when wanting more than 3 levels (as you
validly said, all but the leaf level ought to be per-vCPU).

Jan


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