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Re: [libvirt] [PATCHv2 1/6] virNodeGetCPUTime: Expose new API



On Mon, 18 Apr 2011 12:30:45 +0100
"Daniel P. Berrange" <berrange redhat com> wrote:

> On Sun, Apr 10, 2011 at 12:58:56PM +0800, Daniel Veillard wrote:
> > On Fri, Apr 08, 2011 at 08:33:12PM +0900, Minoru Usui wrote:
> > > virNodeGetCPUTime: Expose new API
> > > 
> > > Signed-off-by: Minoru Usui <usui mxm nes nec co jp>
> > > ---
> > >  include/libvirt/libvirt.h.in |   64 ++++++++++++++++++++++++++++++++++++++++++
> > >  src/libvirt_public.syms      |    5 +++
> > >  2 files changed, 69 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
> > > index bd36015..154c138 100644
> > > --- a/include/libvirt/libvirt.h.in
> > > +++ b/include/libvirt/libvirt.h.in
> > > @@ -228,6 +228,57 @@ struct _virNodeInfo {
> > >      unsigned int threads;/* number of threads per core */
> > >  };
> > >  
> > > +/**
> > > + * virNodeCpuTime:
> > > + *
> > > + * a virNodeCpuTime is a structure filled by virNodeGetCpuTime() and providing
> > > + * the information for the cpu time of the node.
> > > + */
> > > +
> > > +/**
> > > + * Cpu Time Statistics Tags:
> > > + */
> > > +typedef enum {
> > > +    /*
> > > +     * The cumulative CPU time which spends by kernel,
> > > +     * when the node booting up.(in nanoseconds).
> > > +     */
> > > +    VIR_NODE_CPU_TIME_KERNEL               = 0,
> > > +    /*
> > > +     * The cumulative CPU time which spends by user processes,
> > > +     * when the node booting up.(in nanoseconds).
> > > +     */
> > > +    VIR_NODE_CPU_TIME_USER                 = 1,
> > > +    /*
> > > +     * The cumulative idle CPU time,
> > > +     * when the node booting up.(in nanoseconds).
> > > +     */
> > > +    VIR_NODE_CPU_TIME_IDLE                 = 2,
> > > +    /*
> > > +     * The cumulative I/O wait CPU time,
> > > +     * when the node booting up.(in nanoseconds).
> > > +     */
> > > +    VIR_NODE_CPU_TIME_IOWAIT               = 3,
> > > +    /*
> > > +     * The CPU utilization.
> > > +     * The usage value is in percent and 100% represents all CPUs on
> > > +     * the server.
> > > +     */
> > > +    VIR_NODE_CPU_TIME_UTILIZATION          = 4,
> > > +
> > > +    /*
> > > +     * The number of statistics supported by this version of the interface.
> > > +     * To add new statistics, add them to the enum and increase this value.
> > > +     */
> > > +    VIR_NODE_CPU_TIME_NR                   = 5,
> > > +} virNodeCpuTimeTags;
> > > +
> > > +typedef struct _virNodeCpuTime virNodeCpuTime;
> > > +
> > > +struct _virNodeCpuTime {
> > > +    virNodeCpuTimeTags tag;
> > > +    unsigned long long val;
> > > +};
> > 
> >   NACK, the size of an enum is not defined by the C language and
> > hence is compiler dependant. We cannot use it as a component of a
> > structure in the API.
> > 
> > >  /**
> > >   * virDomainSchedParameterType:
> > > @@ -460,6 +511,14 @@ int virDomainMigrateSetMaxSpeed(virDomainPtr domain,
> > >  typedef virNodeInfo *virNodeInfoPtr;
> > >  
> > >  /**
> > > + * virNodeCpuTimePtr:
> > > + *
> > > + * a virNodeCpuTimePtr is a pointer to a virNodeCpuTime structure.
> > > + */
> > > +
> > > +typedef virNodeCpuTime *virNodeCpuTimePtr;
> > > +
> > > +/**
> > >   * virConnectFlags
> > >   *
> > >   * Flags when opening a connection to a hypervisor
> > > @@ -593,6 +652,11 @@ int                     virNodeGetInfo          (virConnectPtr conn,
> > >                                                   virNodeInfoPtr info);
> > >  char *                  virConnectGetCapabilities (virConnectPtr conn);
> > >  
> > > +int                     virNodeGetCpuTime       (virConnectPtr conn,
> > > +                                                 virNodeCpuTimePtr stats,
> > > +                                                 unsigned int nr_stats,
> > > +                                                 unsigned int flags);
> > > +
> > 
> >   I don't understand how the API is suppoed to work. Suppose you want
> > the cumulative CPU time, how do you ask for it ? Seems you can't ! You
> > just ask for a big stucture hoping that on return you may find it within
> > the results. That looks broken to me.
> 
> This is the same design we've used in the virDomainGetMemoryStats,
> virDomainGetBlkioParameters, virDomainGetSchedularParamters without
> any undue trouble.

Yes.

> > 
> >   Either you make a simple API giving back an unsigned long long and
> > you use the virNodeCpuTimeTags as the flag value
> > 
> >   int virNodeGetCpuTime(virConnectPtr conn, unsigned long long *time,
> >                         unsigned int flags);
> > 
> > and the flags indicate the value you're interested into, but in that
> > case you have to ask multiple times. Or you make the VIR_NODE_CPU_TIME_*
> > values a bit field, and you pass an array
> > 
> >   int virNodeGetCpuTime(virConnectPtr conn,
> >                         unsigned long long *stats,
> >                         unsigned int nr_stats,
> >                         unsigned int flags);
> > 
> > where flags is the logical or of the values you are interested into, and
> > the implementation put them in order based on the VIR_NODE_CPU_TIME_*
> > values. But in that case you must fail if one of the statistics is not
> > available.
> 
> I think these are worse because you're relying on ordering of values,
> and not all hypervisors will be able to supply all values. In addition
> it makes this stats API completely different to the other stats APIs
> we have.

OK.
I drop v3 design.

Everyone, how about this v2 patch series? Any other opinions?

> 
> Daniel
> -- 
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-- 
Minoru Usui <usui mxm nes nec co jp>


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