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

[Wei Liu <Wei.Liu2@xxxxxxxxxx>]

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:
> >> >>> On 03.12.12 at 17:29, Wei Liu <Wei.Liu2@xxxxxxxxxx> wrote:
> >> > Regarding Jan's comment in [0], I don't think allowing user to specify
> >> > arbitrary number of levels a good idea. Because only the last level
> >> > should be shared among vcpus, other level should be in percpu struct to
> >> > allow for quicker lookup. The idea to let user specify levels will be
> >> > too complicated in implementation and blow up percpu section (since the
> >> > size grows exponentially). Three levels should be quite enough. See
> >> > maths below.
> >> 
> >> I didn't ask to implement more than three levels, I just asked for
> >> the interface to establish the number of levels a guest wants to
> >> use to allow for higher numbers (passing of which would result in
> >> -EINVAL in your implementation).
> >> 
> > 
> > Ah, I understand now. How about something like this:
> > 
> > struct EVTCHNOP_reg_nlevel {
> >     int levels;
> >     void *level_specified_reg_struct;
> > }
> 
> Yes, just "unsigned int" please.
> 

Right, "unsigned int".

> >> > To sum up:
> >> >      1. Guest should allocate pages for third level evtchn.
> >> >      2. Guest should register third level pages via a new hypercall op.
> >> 
> >> 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).


Wei.

> Jan
> 



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