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Re: [libvirt] [RFD] Add/Modify some API functions about Host Information

Hi, Daniel.

Thank you for your advice.

On Thu, 20 Jan 2011 12:13:21 +0000
"Daniel P. Berrange" <berrange redhat com> wrote:

> On Thu, Jan 20, 2011 at 05:34:28PM +0900, Minoru Usui wrote:
> > Hi, everyone
> > 
> > In an environment with multiple host machines, I want to select a suitable
> > host automatically on which I run a VM depending on machine's load.
> > 
> > Libvirt has APIs to get host machine's information,
> > but I think these APIs aren't enough for above purpose.
> > So I suggest below changes. What do you think?
> > 
> >   * virNodeGetInfo()
> >       This API can get "CPU frequency"(mhz member of virNodeInfo) from
> >       "cpu MHz" of /proc/cpuinfo. 
> >       This value isn't constant, because it may be decrease by
> >       power saving feature.(cf. cpuspeed on RHEL)
> > 
> >       This value is very useful for getting *present* cpu frequency, but I
> >       want to get Maximum CPU frequency, too.
> >       I want to add max_mhz member in struct virNodeInfo from
> >       /sys/device/system/cpu/cpuXX/cpufreq/cpuinfo_max_freq.
> The 'cpu MHz' field should already be reporting the max frequency
> because  the current scaled frequency is pretty much irrelevant
> for making decisions against. If it isn't reporting the max freq
> for some drivers, we should fix that.

I'll try to fix this problem.

> NB, you canot simply add extra fields to the virNodeInfo
> structure because that would break ABI compatibility.

I agree.
I don't want to break ABI compatibility.

> >   * virNodeGetFreeMemory()
> >     This API returns amount of free memory of the host machine's all
> >     node, but this value doesn't include host's cache/buffer memory.
> >     For above purpose, it would be more suitable to account cache/buffer 
> >     as free memory, because most of cache/buffer memory are reclaimable.
> >     But I think virNodeGetFreeMemory()'s ABI should not change easily.
> >  
> >     I want to add function virNodeGetCacheBufferMemory(). It returns 
> >     amount of cache + buffer memory from /proc/meminfo.
> If we wanted to add API for this kind of information, I think
> we'd likely want to have a more flexible API which we can
> easily extend. eg something that looks like virDomainGetMemoryParameters
> but for the virConnectPtr instead of virDomainPtr.

I'll try to implement virNodeGetMemoryParameters() like virDomainGetMemoryParameters().

> >   * virSysinfoRead()
> >     This API is completely internal.
> >     But DMI type1 information(dmidecode -t1) is useful for above
> >     purpose, because it's one of the information which suppose to
> >     processing capacity about host machine.
> >     
> >     I want to export virSysinfoRead() to user.
> I wouldn't want to export the API, because that would require
> us to expose some complex structures in the public ABI. I
> think we'd just want to expose the data in the host capabilities
> XML, or have an API to query the XML of just the sysinfo on its
> own.
> Regards,
> Daniel
Minoru Usui <usui mxm nes nec co jp>

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