Re: [Xen-devel] [PATCH 1/2] add cpu_thread_id to struct cpuinfo_x86

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.09.18 at 15:53, <jgross@xxxxxxxx> wrote:
> On 03/09/18 15:46, Jan Beulich wrote:
>>>>> On 31.08.18 at 18:22, <jgross@xxxxxxxx> wrote:
>>> Add the thread-id to the cpu config data and an accessor macro
>>> cpu_to_thread().
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>> ---
>>>  xen/arch/x86/cpu/common.c       |  1 +
>>>  xen/arch/x86/smpboot.c          | 10 ++++++++++
>>>  xen/include/asm-arm/processor.h |  1 +
>>>  xen/include/asm-x86/processor.h |  2 ++
>>>  xen/include/public/sysctl.h     |  1 +
>>>  5 files changed, 15 insertions(+)
>>>
>>> diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
>>> index 057859ab14..f626a6a510 100644
>>> --- a/xen/arch/x86/cpu/common.c
>>> +++ b/xen/arch/x86/cpu/common.c
>>> @@ -434,6 +434,7 @@ void identify_cpu(struct cpuinfo_x86 *c)
>>>     c->phys_proc_id = XEN_INVALID_SOCKET_ID;
>>>     c->cpu_core_id = XEN_INVALID_CORE_ID;
>>>     c->compute_unit_id = INVALID_CUID;
>>> +   c->cpu_thread_id = XEN_INVALID_THREAD_ID;
>>>     memset(&c->x86_capability, 0, sizeof c->x86_capability);
>>>  
>>>     generic_identify(c);
>>> diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
>>> index 7e76cc3d68..2c6a40c543 100644
>>> --- a/xen/arch/x86/smpboot.c
>>> +++ b/xen/arch/x86/smpboot.c
>>> @@ -247,6 +247,8 @@ static void set_cpu_sibling_map(unsigned int cpu)
>>>      cpumask_set_cpu(cpu, per_cpu(cpu_core_mask, cpu));
>>>      cpumask_set_cpu(cpu, per_cpu(cpu_sibling_mask, cpu));
>>>  
>>> +    c[cpu].cpu_thread_id = 0;
>>> +
>>>      if ( c[cpu].x86_num_siblings > 1 )
>>>      {
>>>          for_each_cpu ( i, &cpu_sibling_setup_map )
>>> @@ -270,6 +272,14 @@ static void set_cpu_sibling_map(unsigned int cpu)
>>>                         "CPU%u: unclear relationship with CPU%u\n",
>>>                         cpu, i);
>>>          }
>>> +
>>> +        for_each_cpu ( i, per_cpu(cpu_sibling_mask, cpu) )
>>> +        {
>>> +            if ( cpu == i )
>>> +                break;
>>> +            c[cpu].cpu_thread_id++;
>> 
>> No. This wants doing alongside setting of the other similar fields,
>> i.e. in (at least) detect_extended_topology() and detect_ht(). It
>> is the hardware which tells us what the thread ID is.
> 
> I wasn't able to find the related information for AMD cpus. In case it
> is in the specs it is hidden very well.

What was used for compute units in Fam16 and earlier is used for
hyperthreads in Fam17 (and going forward, from what iirc Brian
has said).

Jan



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