One versus Two processor question

[mikebore]

The general advice seems to be to use one processor normally and two if the application/usage pattern requires it.

So my question is "does switching between one and two processors on the same VM require re-activation each time?"

I am using an evaluation license for Fusion, and in my 30 day pre-activation on the Vista install so can't try for myself.

Any other comments about one versus two processors welcome.

Thanks

Mike

[aliasme]

Short Version:

Two processors is 1.5-2x as fast

Only Mac Pros should use dual processors, not laptops

Only heavy multitaskers (more than 4-5 applications needing lots of cpu time) or applications with large processing loads will really benefit, but they will benefit.

---

Long version (I wrote this first ha ha):

Performance wise, there is clearly a difference in the performance of one versus two processors for certain types of operations. I read a post on Parallels where they were claiming two processors is trickery because the guest OS is just treated as another application that kicks off threads that OS X will distribute if necessary. This information and speculation on the Parallels forum is incorrect. When you benchmark Fusion with cpu clock independent tools, the performance is 1.5-2x as fast on certain operations. That's a lot!

If you are launching Fusion to write Word docs and use Excel you probably won't notice any difference. If you are opening 10 apps, and 1 or more are multithreaded apps that require a lot of background processing, or apps that performance large computational tasks then you will benefit from the multiprocessor config.

Also, this only really works on the Mac Pro. Since Fusion ties itself to two cores on one processor, the Mac Pro has another chip and two cores to use for other tasks. On the Macbook Pro or other machines, using two cores of 1 chip in the OS client will cause contentious, "spin-lock" conflicts (as described by one of the VMware engineers).

To answer your question, no I do not think you have to activate Windows after the processor configuration change.

[admin]

Also, this only really works on the Mac Pro. Since

Fusion ties itself to two cores on one processor, the

Mac Pro has another chip and two cores to use for

other tasks.

Actually, I don't think OS X gives us the ability to specify which core(s) we're running on. Mac Pros might be a win because there are more cores to run on, but I think there's still contention on a Mac Pro, and you'll still see an improvement (assuming the rest of the system lightly loads the CPU) for such multiprocessor-advantaged programs on other Macs.

Disclaimer: Like a lot of what I say, this is outside my area of expertise and may be incorrect.

[Andreas_Masur]

Actually, I don't think OS X gives us the ability to

specify which core(s) we're running on. Mac Pros

might be a win because there are more cores to run

on, but I think there's still contention on a Mac

Pro, and you'll still see an improvement (assuming

the rest of the system lightly loads the CPU) for

such multiprocessor-advantaged programs on other

Macs.

Disclaimer: Like a lot of what I say, this is outside

my area of expertise and may be incorrect.

Actually you are quite right...'ksc' actually provide a more technical insight[/url] to the whole 1 vs. 2 vCPU game once...

Ciao, Andreas

[Pat_Lee]

KSC does provide great coverage in that post. From what I have seen, it truly depends on the applications of the advantages 2-day Virtual SMP provides.

For general use in Word, Excel, and using Windows in general, it will mean little for many people.

However, if you are using or developing applications that are highly parallel and can use multiple processors there can be a serious advantage of using 2-way virtual SMP. See the CNET benchmarks from earlier this week for a great example of where it helps. VMware Fusion is up to 4 times faster than Parallels on some tests due to 2-way SMP:

http://crave.cnet.com/8301-1_105-9760910-1.html

Mind you, the benefit of 2-way virtual SMP will be seen by users of Mac Pros that have 4 or 8 cores because they have extra, available cores so we can leverage two cores while Mac OS X and other applications take advantage of the other cores on the Mac.

On a dual-core only Mac, you will not see much of a performance boost from 2-way Virtual SMP since Mac OS X is taking up a good chunk of one core to run the OS and applications like Fusion.

Hope this helps.

Pat

[mikebore]

Thanks all for the info and links.

I have done some benchmarking of one versus two in Vista using Passmark, on my core duo 1.83 Macbook pro with 2 Gb RAM, and found the CPU scores to improve by the 1.5x typical as mentioned, but the 2D graphics scores to go down by a similar amount, as mentioned on the linked thread.

I want to use Fritz Chess which supports multiprocessors, but not Vista. I will try XP tomorrow but anticipate that Fritz should really benefit from two processors.

In answer to my main question aliasme wrote:

"To answer your question, no I do not think you have to activate Windows after the processor configuration change."

Can anyone confirm this? I seem to remember reading somewhere that it did cause reactivation but can't find it again.

Thanks again

Mike

[faisalrq]

I am new to VMWare so my apologies if my question doesn't make any sense. Considering that VMWare only allows us to pick up to 2 processors, If i have Quad Core processor and guest OS needs more than 2 processor's power, how I can make it happen.

Other question is if I have mulitple VM Operating Systems running on such hardware how do I know they are making use of all 4 cores and its not just 1 or 2 cores serving all VM machines.. I think this question should be asked in Intel forum but just want to get an idea .... is there any feature in VMWare that can dedicate Dual or Quad core processors to make use of all of their cores availble.

Thanks in advance.

[admin]

It's not clear what you're asking. On VMware's hosted products, the maximum number of CPUs you can give to a guest is 2 (virtual CPUs, which are cores, not the actual CPU). So you can't dedicate more than that because that's the maximum. If you run more than one guest (perhaps your app can be parallelized across multiple virtual CPUs), you will benefit. You can check that the extra cores are actually being used by watching Activity Monitor.