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

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

There is also no need to copy whole op to user at the end, max_cpu_index is

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

Can't those components dlopen libxl? That's what I was assuming we'd do with hwlock.


+            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.


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