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

[Zdenek Styblik]

On 01/20/2011 09:34 AM, 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.
> 
>   * 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.
> 
>   * 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.

Hello,

this is a great news. I was wondering if libvirt has anything like load
balancing(or HA). I'm not sure if this is aim of yours resp. of this
RF(C|D).

Anyway, wouldn't it be better to count in total load, io-waits, idle
etc. instead of just CPU freq?

I agree with memory as being key element, still I would choose by more
just than these two. I mean, machine can have "low" CPU utilization,
perhaps even "a lot" of free RAM, yet high io-waits. I wouldn't want to
migrate anything there.

It might be as well as gibberish/rubbish from my side, or plain
misunderstanding. I beg for forgiveness! :)

Regards,
Zdenek

-- 
Zdenek Styblik
Net/Linux admin
OS TurnovFree.net
email: stybla at turnovfree.net
jabber: stybla at jabber.turnovfree.net