Re: [RFC PATCH 00/10] ppc/pnv: Better big-core model, lpar-per-core, PC unit

["Nicholas Piggin" <npiggin@gmail.com>]

On Mon May 27, 2024 at 4:25 PM AEST, Cédric Le Goater wrote:
> On 5/26/24 14:26, Nicholas Piggin wrote:
> > Primary motivation for this series is to improve big-core support.
> > Other things like SPR indirect, timebase state, PC xscom, are required
> > for minimal big core support.
> > 
> > I'm still not 100% happy with the big-core topology model after this.
> > Maybe one day we add pnv big core and pnv small core structures. But
>
> I haven't look at the proposal yet, but indeed, we could introduce
> a new TYPE_PNV_CORE type for big cores only.

Yeah. It's still tricky because big-core structure contains the CPUs
if you are running in small core mode. So it would really have to be
a PnvCPUCore and PnvPervasiveCore or something, where the former is
either SMT4 and 1:1 with the latter or SMT8 and 1:2 depending on mode.

And some of the "CPU" type operations in big core mode still need to
operate on the small core.

For now, the accessors and helpers seem to be not too bad.

> > nothing is completely clean because big core mode still has certain
> > small core restrictions. I think for now we take a bit of mostly
> > abstracted ugliness in TCG code for the benefit of not spreading
> > hacks through pervasive (xscom) core addressing.
> > 
> > After this series, power9 and power10 get through skiboot/Linux boot
> s
>
> Have you tried SMT8 on powernv8 ? I remember seeing a hang if I am correct.
> I don't think POWER8 deserves much attention anymore, we could deprecate
> POWER8E and POWER8NVL. However, we should at least report an error if we
> know a setup is broken.

Yeah it does have some problem. Maybe should just disable SMT unless
someone finds time to work it out.

Thanks,
Nick