Re: [PATCH v5 3/8] sysctl: Make XEN_SYSCTL_topologyinfo sysctl a little more efficient

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 03/20/2015 09:25 AM, Ian Campbell wrote:
> On Thu, 2015-03-19 at 17:53 -0400, Boris Ostrovsky wrote:
> [...]
>> * Replace INVALID_TOPOLOGY_ID with "XEN_"-prefixed macros for each invalid type
>>    (core, socket, node).
> But not for distance:
>
>> @@ -1375,7 +1360,7 @@ static PyObject *pyxc_numainfo(XcObject *self)
>>           for ( j = 0; j <= max_node_index; j++ )
>>           {
>>               uint32_t dist = nodes_dist[i*(max_node_index+1) + j];
>> -            if ( dist == INVALID_TOPOLOGY_ID )
>> +            if ( dist == ~0u )
> ?

This patch replaces INVALID_TOPOLOGY_ID with 
XEN_INVALID_CORE/SOCKET/NODE_ID for CPU topology. Neither of those would 
be appropriate for distance.

OTOH, the hypervisor never actually returns INVALID_TOPOLOGY_ID for 
"bad" distance -- it explicitly sets the value to ~0u (see 
XEN_SYSCTL_numainfo in do_sysctl()). Thing work since 
INVALID_TOPOLOGY_ID happens to be defined as ~0u, but only by accident.

The next patch (4/8) introduces XEN_INVALID_NODE_DIST and updates the 
hypervisor to report this value when distance is not available. And the 
hunk above is updated to use it as well.

Andrew noticed this too when reviewing previous version so it may be 
worth mentioning in the commit message.

-boris

>
> Other than that the tools side here looks ok.
>