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

["Cédric Le Goater" <clg@kaod.org>]

On 5/27/24 09:32, Nicholas Piggin wrote:
> 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.


The new _init routines would be a good place to do that.

Thanks,

C.


> 
> Thanks,
> Nick