Re: [PATCH v11 3/4] arm64: topology: Support SMT control on ACPI based system

Yicong Yang
2025-03-03T14:43:05Z

On 2025/3/3 19:16, Sudeep Holla wrote:
> On Mon, Mar 03, 2025 at 10:56:12AM +0100, Pierre Gondois wrote:
>> On 2/28/25 20:06, Sudeep Holla wrote:
>>>>>
>>>>> Ditto as previous patch, can get rid if it is default 1.
>>>>>
>>>>
>>>> On non-SMT platforms, not calling cpu_smt_set_num_threads() leaves
>>>> cpu_smt_num_threads uninitialized to UINT_MAX:
>>>>
>>>> smt/active:0
>>>> smt/control:-1
>>>>
>>>> If cpu_smt_set_num_threads() is called:
>>>> active:0
>>>> control:notsupported
>>>>
>>>> So it might be slightly better to still initialize max_smt_thread_num.
>>>>
>>>
>>> Sure, what I meant is to have max_smt_thread_num set to 1 by default is
>>> that is what needed anyways and the above code does that now.
>>>
>>> Why not start with initialised to 1 instead ?
>>> Of course some current logic needs to change around testing it for zero.
>>>
>>
>> I think there would still be a way to check against the default value.
>> If we have:
>> unsigned int max_smt_thread_num = 1;
>>
>> then on a platform with 2 threads, the detection condition would trigger:
>> xa_for_each(&hetero_cpu, hetero_id, entry) {
>> if (entry->thread_num != max_smt_thread_num && max_smt_thread_num) <---- (entry->thread_num=2) and (max_smt_thread_num=1)
>> pr_warn_once("Heterogeneous SMT topology is partly
>> supported by SMT control\n");
>>
>> so we would need an additional variable:
>> bool is_initialized = false;
>
> Sure, we could do that or skip the check if max_smt_thread_num == 1 ?
>
> I mean
> if (entry->thread_num != max_smt_thread_num && max_smt_thread_num != 1)
>

this will work for me. will launch some tests.

Thanks.