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Re: [libvirt] [PATCHv6 0/6] Add virNodeGetCPUStats() API



On Fri, May 27, 2011 at 02:34:50PM +0100, Daniel P. Berrange wrote:
> On Wed, May 25, 2011 at 03:01:29PM +0900, Minoru Usui wrote:
> > Hi,
> > 
> > This is v6 of virNodeGetCPUTimeParameters() API. 
> > (This time, I rename it to virNodeGetCPUStats())
> > It returns cpu utilization or 
> > cumulative cpu time of the node from /proc/stat since node boots up.
> > This patch only supports linux host.
> 
> The code in this patch series looks fine to me now. I would
> ACK the whole series, but I have one design question I should
> have asked previously.
> 
> This API returns CPU information for the host as a whole.
> Historically, when adding an API like this, someone has always
> then asked for a per-CPU breakdown of the same data.
> 
> So I wonder if we should add a parameter for the CPU num
> to the API:
> 
>  int                     virNodeGetCPUStats (virConnectPtr conn,
>                                              int cpuNum,
>                                              virCPUStatsPtr params,
>                                              int *nparams,
>                                              unsigned int flags);
> 
> And have a constant for getting the host data as a whole:
> 
>    #define  VIR_NODE_CPU_STATS_ALL_CPUS -1
> 
> so if you want to get individual data for each CPU you
> can do
> 
>    virNodeGetCPUStats(conn, 0, params, nparams, flags);
>    virNodeGetCPUStats(conn, 1, params, nparams, flags);
>    virNodeGetCPUStats(conn, 2, params, nparams, flags);
>    virNodeGetCPUStats(conn, 3, params, nparams, flags);
> 
> But if you just want the data for the host as a whole
> you can do
> 
>    virNodeGetCPUStats(conn, VIR_NODE_CPU_STATS_ALL_CPUS,
>                       params, nparams, flags);
> 
> The /proc/stat file already has the data we need for both
> these styles
> 
> $ grep cpu /proc/stat 
> cpu  2632143 17400 1341532 32819705 1177560 674 21606 0 11997 0
> cpu0 1263069 9280 596278 16274365 620428 631 17303 0 6131 0
> cpu1 1369073 8119 745254 16545339 557131 43 4302 0 5865 0

  Agreed, similary as for the virNodeGetMemoryStats() patch set, the
patches looks good enough for being applied but doing the suggested
changes (i.e. adding a new argument for the cpu number or the cell
number).
  For virsh command I would make querying all the default but just
add an optionnal argument --cpu
    virsh nodecpustats --cpu cpunumber
and similary on the memry patch set add an optional --cell argument
    virsh nodememstats --cell cellnumber

 That way the API and virsh command are ready for more precise use
and we won't need to make a second set of APIs.

  thanks !

Daniel
-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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