Re: [PATCH] xen/arm: Set correct per-cpu cpu_core_mask

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Henry,

On 08/03/2024 03:05, Henry Wang wrote:
> Hi everyone,
> 
> On 2/26/2024 6:43 PM, Michal Orzel wrote:
>>>>>   xen/arch/arm/smpboot.c | 6 +++++-
>>>>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>
>>>>> +    /* PE not implemented using a multithreading type approach. */
>>>>> +    if ( system_cpuinfo.mpidr.mt == 0 )
>>>> Do we need this check? It mt was true, cpu_sibling_mask would be incorrect
>>>> anyway (it would still be 1).
>>> I added this check for playing safe, because I only want to do the correct 
>>> thing
>>> in this patch and avoid make things worse for MT case. With this patch, 
>>> non-MT
>>> case can be improved and the MT case is remain unchanged.
>>>
>>> But I agree with you, and I would be more than happy if I can run a MT 
>>> setup and
>>> finish the "else" part with this patch or follow-ups. Do you know maybe 
>>> qemu can
>>> allow me to emulate a MT setup so that I can fix it properly in v2? Thanks!
>> A65 is the only Arm CPU with SMT and I'm not aware of Qemu being able to 
>> emulate it.
>> AFAICT, in Xen on Arm we assume no SMT, hence my question about your check. 
>> With or without it,
>> some parts would still be incorrect (like cpu_sibling_mask), so what's the 
>> point in having a partial check.
>> I would keep your solution without the check. Others may have a different 
>> opinion though.
> 
> Since there isn't much discussion followed-up in this thread, I am 
> wondering do we have more inputs/opinions on this topic? If everyone 
> agrees, I've followed Michal's suggestion in v2 [1].
I clearly forgot to say in v2 that I'm ok with this change, so:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal