[libvirt] [RFC][PATCHv1 2/5] libvirt - new API for getting percpu statistics of VM

[KAMEZAWA Hiroyuki]

On Sat, 16 Apr 2011 14:52:51 +0100
"Richard W.M. Jones" <rjones at redhat.com> wrote:

> On Fri, Apr 15, 2011 at 04:04:52PM +0900, KAMEZAWA Hiroyuki wrote:
> [...]
> 
> The idea and the implementation is sound.  However I have a problem
> with this proposed API:
> 
> > +typedef struct _virDomainPcpuStat virDomainPcpuStatStruct;
> > +
> > +struct _virDomainPcpuStat {
> > +    unsigned long long cpuTime;
> > +};
> > +
> > +typedef virDomainPcpuStatStruct *virDomainPcpuStatPtr;
> 
> [...]
> 
> >  /**
> > + * virDomainPcpuStats:
> > + * @dom: pointer to the domain object
> > + * @stats: nr_stats-sized array of stat structures (returned)
> > + * @nr_stats: number of cpu statistics requested
> > + * @flags: unused, always pass 0
> > + *
> > + * This function provides per-cpu statistics for the domain. 'cpu' here means
> > + * not vcpu.
> > + *
> > + * Up to 'nr_stats' elements of 'stats' will be populated with cpu statistics
> > + * from the domain.  Only statistics supported by the domain, the driver, and
> > + * this version of libvirt will be returned.
> > + *
> > + * Now, only cpuTime per cpu is reported in nanoseconds.
> > + *
> > + * Returns: The number of stats provided or -1 in case of failure.
> > + */
> > +int virDomainPcpuStats (virDomainPtr dom, virDomainPcpuStatPtr stats,
> > +                          unsigned int nr_stats, unsigned int flags)
> 
> Am I correct that the caller sets nr_stats == number of physical
> cores, and allocates an array of nr_stats * virDomainPcpuStats
> structs?
> 
> We could never add more elements to the _virDomainPcpuStat structure,
> because that would break the ABI for existing callers.  (Or I guess we
> could use the flags field).
> 
> I think we should forget about the structure, and just use an array of
> unsigned long long's, but I'd like to hear what others think.
> 

I received the same reply from others and I'd like to go that way.


> Is it likely that we would return other per-physical-CPU stats in
> future?
> 

Not sure. But if some guy adds more statistics to cpuacct cgroup, as
# of vmenter/vmexit etc...we can count it.

So, I'd like to pass 'What you want' flag as

VirDomainPhysicalCpuStat(domain,
			 unsigned long long *starts,
			 int nr_stats,
			 int what_I_want)

and then, pass VIT_DOMAIN_PHYSICAL_CPU_STAT_CPUTIME as it argument. what_I_want.

Thanks,
-Kame