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From Tamas Monos <>
Subject RE: Vmware CPU Cap
Date Tue, 22 May 2012 23:25:30 GMT

I have a service offering with 1000Mhz limit and 4 cpu cores. That sums up to 4000Mhz.
Cloudstack sets the limit to 4Ghz on the virtual machine and when I put load on it vmware
balances the load between the 4 cores allowing them to use 1000Mhz each.
I do not see any bugs here.

Apologies if the "meant per CPU core" was incorrect. What I meant is described above.


-----Original Message-----
From: Edison Su [] 
Sent: 23 May 2012 00:05
Subject: RE: Vmware CPU Cap

Nope, from the document, the limit is set on whole vm:
CPU Limits
When a CPU Limit is set on a virtual machine resource settings, the virtual machine is deliberately
held from being scheduled to a PCPU when it has used up its allocated CPU resource. This happens
regardless of the CPU utilization. If the limit is set to 500MHz, the virtual machine is descheduled
from the PCPU and has to wait before it is allowed to be scheduled again. As such, the virtual
machine might experience performance degradation.
Note: For an SMP virtual machine, the sum of all vCPUs cannot exceed the specified limit.
For example, 4 vCPU virtual machine with a limit of 1200MHz and equal load among vCPUs would
result in a max of 300MHz per vCPU.

> -----Original Message-----
> From: Tamas Monos []
> Sent: Tuesday, May 22, 2012 3:43 PM
> To:
> Subject: RE: Vmware CPU Cap
> Hi,
> No I don't think this is a bug. When you set 1000Mhz as CPU cap that 
> is meant per core. vmWare will limit each CPU core to 1000Mhz.
> As you gave 2 CPU cores that is 2000Mhz effective. That is how vmware 
> works.
> I have setup my offerings all to 1000Mhz as speed and just increasing 
> the number of cores.
> 1 core ends up being 1x1000Mhz
> 2 core ends up being 2x1000Mhz=2000Mhz ...
> ...
> I'm actually using it in production and works quite well as Cloudstack 
> "allocates" 4000Mhz when I'm using 4x1000Mhz cores and vmware cleverly 
> balances between the cores as you put load on it and not letting any 
> of the cores above the set limit of 1000Mhz.
> Regards
> -----Original Message-----
> From: Diego Spinola Castro []
> Sent: 22 May 2012 19:34
> To:
> Subject: Re: Vmware CPU Cap
> I forgot the link:
> 2012/5/22 Diego Spinola Castro <>
> > I believe that is a bug with cpu cap and vmware.
> >
> > To reproduce:
> >
> > Create a offering with 2 cores and 1000mhz.
> > Enable CPU CAP.
> >
> > After created instance , cs create a vm with 2 cores and 1000mhz of
> limit.
> >
> > I don't know for sure if is a bug, but vmware gives 1000mhz shared 
> > with cores.
> >
> >
> >
> > Diego
> >

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