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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan



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