Re: [Xen-devel] [PATCH 2/2] xen: fill topology info for online cpus only

[Juergen Gross <jgross@xxxxxxxx>]

On 30/08/18 10:43, Jan Beulich wrote:
>>>> On 30.08.18 at 10:31, <jgross@xxxxxxxx> wrote:
>> On 30/08/18 10:16, Jan Beulich wrote:
>>>>>> On 29.08.18 at 20:23, <jgross@xxxxxxxx> wrote:
>>>> The topology information obtainable via XEN_SYSCTL_cputopoinfo is
>>>> filled rather weird: the size of the array is derived from the highest
>>>> online cpu number, while the data is set to "invalid" for not present
>>>> cpus only.
>>>>
>>>> With smt=0 the information for parked threads is all zero, so it should
>>>> be best to return "invalid" information for offline cpus.
>>>>
>>>> On a dual core system without this patch xl info -n will print:
>>>>
>>>> cpu_topology           :
>>>> cpu:    core    socket     node
>>>>   0:       0        0        0
>>>>   1:       0        0        0
>>>>   2:       1        0        0
>>>
>>> But there's nothing wrong here. The interesting part is what would be
>>> printed for CPU 3 (perhaps on a more than two cores system). After
>>> all topology is valid irrespective of whether a CPU is online - it all
>>> depends on whether the hypervisor still has the information available.
>>> It is for a reason that cpu_smpboot_free() invalidates certain fields
>>> only upon CPU removal:
>>>
>>>     if ( remove )
>>>     {
>>>         c[cpu].phys_proc_id = XEN_INVALID_SOCKET_ID;
>>>         c[cpu].cpu_core_id = XEN_INVALID_CORE_ID;
>>>         c[cpu].compute_unit_id = INVALID_CUID;
>>>
>>> On a 6-core system I see
>>>
>>> cpu:    core    socket     node
>>>   0:       0        0        0
>>>   1:       0        0        0
>>>   2:       1        0        0
>>>   3:       1        0        0
>>>   4:       2        0        0
>>>   5:       2        0        0
>>>   6:       8        0        0
>>>   7:       8        0        0
>>>   8:       9        0        0
>>>   9:       9        0        0
>>>  10:      10        0        0
>>>
>>> which looks fine to me, apart from the missing info on CPU 11.
>>
>> I can change the patch to print the information for the offline cpus
>> (including the now missing ones), too.
>>
>> What is the preferred solution?
> 
> Well, by implication from my earlier reply I think adding the missing
> CPU's info would be better. Let's see what others think.

Okay.

I'll do that and add another patch adding "(offline)" to the output in
case a cpu is offline.


Juergen

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