The max number of vCPUs per VM we can assign is 4. I assume this is because quad core = 4 core = vCPUs?
First the battle rages on into whether or not more CPU in a VM = more performance. I say not. I also have plenty of supporting documentation and OTHER companies that discourage multi CPU VM's. Despite the small group of people in this forum, it's widely accepted that running more than 1 vCPU in a VM is basically useless, this is in Hyper-V, VM Ware and any other non-paravirtualized environment.
So I question whether or not you will even see any improvement (which you won't) and with that many CPU assigned to a VM I question why you are running in a VM to begin with.
Think about this from a purely logical point of view. One VM, takes over ALL the CPU on the host, what's left for remaining VM's? How about none? Bad move for VM's Also the idea behind VM's isn't to compete for Physical performance, RAM, or size and scope of machines, it's sole purpose is to go green, save space and consolidate management. But if you start stacking the deck, it's a diminishing return on your VM License.
So test first. With 1 vCPU, run a benchmark or two. Then run the SAME benchmark again, this time ONLY make the VM 2 vCPU. I will wager whatever money you have on grant you that the performance (if any, I still say none) will be less than 10%. (Unless it's Linux VM's). Going from 2 or more to 4 or 8 vCPU will definately be ZERO performance.
So first you have to run some test before you think you NEED that many CPU. I think you are mostly stuck on the idea because physical boxes with all those cores, somehow you figure VM's will utlize them the same way, they will not. VM's are basically a bunch of threads running at the same time. So monopolizing the CPU isn't going to give you what you think it will.
Try a bench mark first, and if you actually see improvement, I would like to see the graphs.
EVERY time I ask this question, not one person has actually put up the graphs, charts or the numbers to PROVE their findings. I find that remarkable. I say it's 'theorhetical' and no one can actually show their test results (Linux however does improve a little for 2 CPU). I have compared notes with a few other companies and we are all scratching our heads wondering 'You think people SAY they improve when they really don't?'. I really think that's the bottom line.
People talk a lot, but have yet to show any evidence. But VM Ware will appease the masses by giving them what they want (8 vCPU). Even their engineers (and I have personally talked to a couple) say that it's mostly people with their comfort zones that makes it SEEM better. You just want to believe that 1 CPU isn't enough, so you add more. But just because you CAN do it, and VM ware makes it possible doesn't mean that you will see any improvement.
It's like a child wanting a cookie, they won't stop until you give them what they want. So let them have as many as they want until they get sick, then they won't want any more... Gotta love Psychology.
No evidence, ok 
XP VMs.
time to completion of their testing task (a highly multithreaded task).
1 CPU: 2:11
2 CPU: 1:30
As for our linux VMs, they improve almost linearly with the vCPUs
1) 8:12
2) 4:45
4) 3:34
So, I've got $40 in my pocket right now. I take paypal :).
--M
--Matt
VCP, vExpert, Unix Geek
No, they aren't scheduled.
And different forum members have seen different results, depending on their environment.
Unlike mcgower, we only see performance issues (not benefit) using multiple vCPUs.
It really all depends on your workload, your hosts, and your storage...
Jase McCarty
Co-Author of VMware ESX Essentials in the Virtual Data Center
(ISBN:1420070274) from Auerbach
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