Re: [Xen-devel] Hwloc with Xen host topology

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>]

Andrew Cooper, le Thu 02 Jan 2014 22:01:30 +0000, a écrit :
> On 02/01/14 21:55, Samuel Thibault wrote:
> > Andrew Cooper, le Thu 02 Jan 2014 21:50:06 +0000, a écrit :
> >> On 02/01/14 21:24, Samuel Thibault wrote:
> >>> Andrew Cooper, le Thu 02 Jan 2014 20:26:49 +0000, a écrit :
> >>>> Cores are numbered per-socket in Xen, while sockets,
> >>>> numa nodes and cpus are numbered on an absolute scale.  There is
> >>>> currently a gross hack in my hwloc code which adds (socket_id *
> >>>> cores_per_socket * threads_per_core) onto each core id to make them
> >>>> similarly numbered on an absolute scale.  This is fine for a homogeneous
> >>>> system, but not for a hetrogeneous system.
> >>> BTW, hwloc does not need these physical ids to be unique, it can cope
> >>> with duplication and whatnot.  That said, having a coherent interface at
> >>> the Xen layer would be a good thing, indeed :)
> >> If I take out the described hack, I am presented with
> >>
> >> ****************************************************************************
> >> * hwloc has encountered what looks like an error from the operating system.
> >> *
> >> * object (Core P#0 cpuset 0x30000003) intersection without inclusion!
> >> * Error occurred in topology.c line 853
> >> *
> >> * Please report this error message to the hwloc user's mailing list,
> >> * along with the output from the hwloc-gather-topology.sh script.
> >> ****************************************************************************
> >>
> >> Which I took to mean "I have done something stupid".  I looked and saw
> >> that I was attempting to insert a second Core P#0 object with a
> >> different cpuset and decided to renumber the cores so they didn't
> >> overlap in physical ids.
> >>
> >> If you believe that this should indeed work, then I guess I need to
> >> raise a bug...
> > Well, logical processor physical ids, i.e. what is used for indexing
> > physical cpusets, have to be unique. The core/socket/node IDs don't have
> > to.
> 
> Then a bug needs raising.  My hack only changes the Core physical ID as
> far as hwloc is concerned.  The PU physical IDs are unchanged by the
> hack, and already unique as presented by Xen.

This needs investigation indeed.  I'm sure we are supposed to support
that kind of case.

Samuel

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