On Wed, May 02, 2012 at 01:43:03PM -0600, Eric Blake wrote:
On 04/24/2012 03:20 AM, Hu Tao wrote:
Currently virDomainGetCPUStats gets total cpu usage, which consists of:
1. vcpu usage: the physical cpu time consumed by virtual cpu(s) of domain 2. hypervisor: `total cpu usage' - `vcpu usage'
The flag VIR_DOMAIN_CPU_STATS_VCPU is for getting vcpu usages. --- include/libvirt/libvirt.h.in | 8 ++++++++ src/libvirt.c | 9 +++++++-- tools/virsh.c | 16 +++++++++++----- 3 files changed, 26 insertions(+), 7 deletions(-)
Question: is it better to make the user call virDomainGetCPUStats twice (once for total with flags==0, once for vcpu with flags=VCPU), where there is a race between the two calls? Or should we instead return both counts in the same call, by having two separate virTypedParameter stat names and no flag?
Slightly off-topic ... My opinion on this -- and it applies to many libvirt calls -- is that APIs where you have to call them twice, once to size the result, and a second time to get the result, are obtuse and hard to use. In libguestfs I took the approach that all calls return malloc'd strings, arrays, etc of the right size. The caller has to free the data, but that's the lesser of two evils. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org