Re: [Xen-devel] [PATCH v2 2/4] sysctl: Make XEN_SYSCTL_topologyinfo sysctl a little more efficient

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/06/2015 08:41 AM, Andrew Cooper wrote:
> On 06/01/15 02:18, Boris Ostrovsky wrote:
> > Instead of copying data for each field in xen_sysctl_topologyinfo separately
> > put cpu/socket/node into a single structure and do a single copy for each
> > processor.
> >
> > There is also no need to copy whole op to user at the end, max_cpu_index is
> > sufficient
> >
> > Rename xen_sysctl_topologyinfo and XEN_SYSCTL_topologyinfo to reflect the fact
> > that these are used for CPU topology. Subsequent patch will add support for
> > PCI topology sysctl.
> >
> > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> If we are going to change the hypercall, then can we see about making it
> a stable interface (i.e. not a sysctl/domctl)?  There are non-toolstack
> components which might want/need access to this information.  (i.e. I am
> still looking for a reasonable way to get this information from Xen in
> hwloc)
Can't those components dlopen libxl? That's what I was assuming we'd do 
with hwlock.
> > <snip>
> >
> > +            if ( cpu_online(i) )
> >               {
> > -                uint32_t socket = cpu_online(i) ? cpu_to_socket(i) : ~0u;
> > -                if ( copy_to_guest_offset(ti->cpu_to_socket, i, &socket, 1) )
> > -                    break;
> > +                cputopo.core = cpu_to_core(i);
> > +                cputopo.socket = cpu_to_socket(i);
> > +                cputopo.node = cpu_to_node(i);
> >               }
> > -            if ( !guest_handle_is_null(ti->cpu_to_node) )
> > +            else
> > +                cputopo.core = cputopo.socket =
> > +                    cputopo.node = INVALID_TOPOLOGY_ID;
> > +
> In particular, can we fix this broken behaviour.  The cpu being online
> or not has no bearing on whether Xen has topology information, and a
> side effect is that when the cpu governer powers down a cpu, it
> disappears from the reported topology.
Yes, I should fix that as well.

-boris


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