[libvirt] [PATCHv2 3/3] virsh: Use virNodeGetCPUMap if possible

[Eric Blake]

On 10/31/2012 08:58 PM, Hu Tao wrote:
> On Wed, Oct 31, 2012 at 06:20:58PM +0100, Viktor Mihajlovski wrote:
>> Modified the places where virNodeGetInfo was used for the purpose
>> of obtaining the maximum node CPU number. Transparently falling
>> back to virNodeGetInfo in case of failure.
>> Wrote utility function vshNodeGetCPUCount to compute node CPU
>> number.
>>

>> +static int
>> +vshNodeGetCPUCount(virConnectPtr conn)
>> +{
>> +    int ret;
>> +    virNodeInfo nodeinfo;
>> +
>> +    if ((ret = virNodeGetCPUMap(conn, NULL, NULL, 0)) < 0) {
>> +        /* fall back to nodeinfo */
>> +        if (virNodeGetInfo(conn, &nodeinfo) == 0) {
>> +            ret = VIR_NODEINFO_MAXCPUS(nodeinfo);
>> +        }
> 
> Isn't VIR_NODEINFO_MAXCPUS buggy? Either don't fall back to nodeinfo
> or fix it.

Hmm, and I just realized another issue - on the RHEL 5 box I tested,
there is no /sys/devices/system/cpu/possible, so virNodeGetCPUCount()
currently fails, even though virNodeGetInfo() succeeded.  I'm going to
hold off pushing this series until after 1.0.0, to avoid any chance of a
last-minute unintentional regression.

You were asking about VIR_NODEINFO_MAXCPUS:

#define VIR_NODEINFO_MAXCPUS(nodeinfo)
((nodeinfo).nodes*(nodeinfo).sockets*(nodeinfo).cores*(nodeinfo).threads)

I can confirm that virNodeGetInfo misbehaves if enough trailing cpus are
offline, and therefore agree that we need to fix that API:

# virsh nodeinfo
CPU model:           x86_64
CPU(s):              2
CPU frequency:       2801 MHz
CPU socket(s):       1
Core(s) per socket:  2
Thread(s) per core:  1
NUMA cell(s):        1
Memory size:         3941792 KiB

# echo 0 > /sys/devices/system/cpu/cpu1/online

# virsh nodeinfo
CPU model:           x86_64
CPU(s):              1
CPU frequency:       2801 MHz
CPU socket(s):       1
Core(s) per socket:  1
Thread(s) per core:  1
NUMA cell(s):        1
Memory size:         3941792 KiB

That just changed things from 2 to 1.  No fun.

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

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