[libvirt] [PATCH 1/3] nodeinfo: Add check and workaround to guarantee valid cpu topologies

[Eric Blake]

On 11/07/2012 08:22 AM, Peter Krempa wrote:
> Lately there were a few reports of the output of the virsh nodeinfo
> command being inaccurate. This patch ties to avoid that by checking if

s/ties/tries/

> the topology actualy makes sense. If it doesn't we then report a

s/actualy/actually/

> synthetic topology that indicates to the user that the host capabilities
> should be checked for the actual topology.
> ---
>  src/nodeinfo.c | 37 +++++++++++++++++++++++++++++++------
>  1 file changed, 31 insertions(+), 6 deletions(-)

You've convinced me that we need this; and we have already documented
that nodes=1 is a hint that the user must verify with the capability XML
for accurate results anyway.  ACK if you can answer one question:

> @@ -531,6 +539,23 @@ done:
>          goto cleanup;
>      }
> 
> +    /* Now check if the topology makes sense. There are machines that don't
> +     * expose their real number of nodes or for example the AMD Bulldozer
> +     * architecture that exposes their Clustered integer core modules as both
> +     * threads and cores. This approach throws off our detection. Unfortunately
> +     * the nodeinfo structure isn't designed to carry the full topology so
> +     * we're going to lie about the detected topology to notify the user
> +     * to check the host capabilities for the actual topology. */
> +    if ((nodeinfo->nodes *
> +         nodeinfo->sockets *
> +         nodeinfo->cores *
> +         nodeinfo->threads) != (nodeinfo->cpus + offline)) {
> +        nodeinfo->nodes = 1;
> +        nodeinfo->sockets = nodeinfo->cpus;
> +        nodeinfo->cores = 1;

Would it be any better to swap these and expose sockets == 1 and cores
== cpus when we fake things?

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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