While waiting for VUM to finish up on some new vSphere ESX 4.0 hosts, I was reading VMTN blogs and noticed this interesting article by Jason Boche: http://www.boche.net/blog/index.php/2009/08/18/hidden-virtual-cpu-limit-restriction-in-esx-3-5/

This script will query a specific cluster and extract out the number of vCPU for the given cluster, each individual host and the advanced configuration Misc.RunningVCpuLimit set for each host.

In ESX 3.5 as Jason pointed out the default is 128 with maximum support of 192 and with vSphere ESX 4.0, this has changed to default of 512

Requirement:
VI Toolkit for Perl/vSphere SDK for Perl/VIMA 1.0/vMA 4.0
vCenter 2.5 / 4.0

Sample Execution:

On ESX 3.5:

[vi-admin@scofield]$ ./getNumofvCPUInCluster.pl --server reflex.primp-industries.com --username primp --cluster primp-cluster
This could take a few minutes depending on the size of the cluster ...

Cluster: primp-cluster
	Host: primp-esx01
		Misc.RunningVCpuLimit: 128
		# of vCPU on host: 12
	Host: primp-esx02
		Misc.RunningVCpuLimit: 128
		# of vCPU on host: 13
	Host: primp-esx03
		Misc.RunningVCpuLimit: 128
		# of vCPU on host: 16
	Host: primp-esx04
		Misc.RunningVCpuLimit: 128
		# of vCPU on host: 16
      ..........
      # of vCPU: 463

On ESX 4.0:

[vi-admin@scofield]$ ./getNumofvCPUInCluster.pl --server mauna-loa.primp-industries.com --username primp --cluster primpProd-cluster
This could take a few minutes depending on the size of the cluster ...

Cluster: primp-cluster
	Host: primp-esx01
		Misc.RunningVCpuLimit: 512
		# of vCPU on host: 21
	Host: primp-esx02
		Misc.RunningVCpuLimit: 512
		# of vCPU on host: 22
      # of vCPU: 23