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

[Juergen Gross <jgross@xxxxxxxx>]

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?


Juergen

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel