Re: [Qemu-devel] [PATCH v5 11/36] spapr/xive: use the VCPU id as a NVT identifier

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Nov 29, 2018 at 04:27:31PM +0100, Cédric Le Goater wrote:
> [ ... ] 
> 
> >>>> +/*
> >>>> + * The allocation of VP blocks is a complex operation in OPAL and the
> >>>> + * VP identifiers have a relation with the number of HW chips, the
> >>>> + * size of the VP blocks, VP grouping, etc. The QEMU sPAPR XIVE
> >>>> + * controller model does not have the same constraints and can use a
> >>>> + * simple mapping scheme of the CPU vcpu_id
> >>>> + *
> >>>> + * These identifiers are never returned to the OS.
> >>>> + */
> >>>> +
> >>>> +#define SPAPR_XIVE_VP_BASE 0x400
> >>>
> >>> 0x400 == 1024.  Could we ever have the possibility of needing to
> >>> consider both physical NVTs and PAPR NVTs at the same time?  
> >>
> >> They would not be in the same CAM line: OS ring vs. PHYS ring. 
> > 
> > Hm.  They still inhabit the same NVT number space though, don't they?
> 
> No. skiboot reserves the range of VPs for the HW at init.
> 
> https://github.com/open-power/skiboot/blob/master/hw/xive.c#L1093

Uh.. I don't see how they're reserved is relevant.

What I mean is that the ENDs address the NVTs for HW endpoints by the
same (block, index) tuples as the NVTs for virtualized endpoints, yes?

> > I'm thinking about the END->NVT stage of the process here, rather than
> > the NVT->TCTX stage.
> >
> > Oh, also, you're using "VP" here which IIUC == "NVT".  Can we
> > standardize on one, please.
> 
> VP is used in Linux/KVM Linux/Native and skiboot. Yes. it's a mess. 
> Let's have consistent naming in QEMU and use NVT. 

Right.  And to cover any inevitable missed ones is why I'd like to see
a cheatsheet giving both terms in the header comments somewhere.

[snip]

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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