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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Aug 30, 2018 at 10:31:16AM +0200, Juergen Gross 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.
> 

That is fine too. I just don't like inconsistent output. :p

P.S. you probably want to add a new field to the existing interface to
indicate if a cpu is online.

Wei.

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