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bob August 9, 2006 14:28

How many licenses for dual core processors?

We plan to purchase a cluster with AMD dual core processors. Does anyone know how many parallel STAR-CD licenses you need for a dual core processor?


Ben August 9, 2006 16:18

Re: How many licenses for dual core processors?
It depends how many jobs you want to run, remember that a dual core is just 2 cpus on one chip (although with only one memory controler) so if you run it as a single serial job then you will just use one of the cpu's but you can run 2 jobs on the same chip. So for example if you have a cluster with 8 dual core chips you actually have 16 cpus and therefore can run a parllel job on all 16 (but will also need 16 parallel licenses). As I say you have to get the idea of it being 1 chip out of your mind.

In reality 1 dual core chip is actually not as efficient as 2 single core chips (for CFD at least) as you are moving the same large amount of memory though one controller instead of 2 and so have a bit of a bottleneck, think of heavy traffic on a two lane motorway with a stretch of single lane somewhere down the line, now think of how much easier the cars would be to travel if the single lane stretch wasnt there! Although this is somewhat irrelevant as AMD are going to stop producing single core opterons fairly soon (the latest single core chip is their last new one) and I am sure Intel will follow suit.

bob August 10, 2006 07:00

Re: How many licenses for dual core processors?
Thanks for your reply, Ben.

Since a dual core processor is not as efficient as 2 single core processors, it wouldn't make sense for us to use a dual core processors with 2 parallel licenses.

If we use the dual core processor to run a single serial job with 1 license, will it be faster than a single core processor? Also, how do you run a single serial job on the dual core? Do you just turn off the dual core function somehow?

Ben August 10, 2006 07:42

Re: How many licenses for dual core processors?
I don't think that you can say that it wouldn't make sense, there are a lot of other factors involved. Firstly, although a 2 cpu job on dual core chip won't be as fast as on 2 single core chip it wont be a huge amount slower (have a look at some benchmarks), we are not talking 20-50% slower, maybe 5%.

If you can get a box with 2/4 single core chips of the same clock speed as a box with 1/2 dual core chips go with the single core box, price being no object. What you will probably find is that the dual core configuration is cheaper and quite possibly has a higher clock speed, so you just have to weigh up your priorities (or those of your accountant)

On the second bit, if you run a serial job on a dual core chip (assuming there are no other high memory apps on the other core and that the clock speeds are the same) then there should be no difference in speed from one to the other.

You run a serial job on a dual core in exactly the same way as you would on a single core chip, you dont turn anything off you dont do anything special. Same as if you were running a serial job on a box with 2 single core chips in it. It all sounds a little confusing but you have to get the idea of a dual core chip being anything amazingly special, its just 2 cpus on one bit of metal as opposed to two, other than that they work the same as any other CPU on the market.

TG August 10, 2006 13:39

Re: How many licenses for dual core processors?
Bob, You can't use 2 cores on a single serial job. 1 serial job means one process on one core (or cpu). If you want to take advantage of dual cores you have 2 choices:

1)Run one parallel job split 2 ways

2)Run 2 serial jobs (1 core each) at the same time.

Either way, you will lose a small amount because both cores will be fighting for resources at the same time.

Just because its not 100% perfectly efficient does not mean you should use 2 cores on a parallel job. Opterons dual cores are quite efficient - 2 cores will probably give you a speed boost of 1.9 out of a possible 2.0. Parallel scaling is never perfectly efficient anyway. Older Intel chips give you alot lets (maybe 1.4 out 2.0) but the new Woodcrest cores compare very favorably with the opteron dual cores.

Ben August 10, 2006 15:28

Re: How many licenses for dual core processors?
I'm sure intel are improving but we have some new intel dual cores at our company and they still don't hold a candle to opterons. AMD were the first to 64 bit and also to dual cores and they just seem to do a better job

TG August 11, 2006 06:49

Re: How many licenses for dual core processors?
Ben - Where those processors specifically Woodcrest? Those are supposed to have a much improved memory bandwidth system which is the main reason that older Intel chips didn't do as well as AMD in the past (not enough bandwidth to handle more than 1 cpu).

airfoil August 11, 2006 14:59

Re: How many licenses for dual core processors?
The lincenses for parallel STAR-CD Star-CD is base on cpu core. If you have single a single socket dual core cpu, you will still need two license for both core. When talking about dual core performance, apart from the controller, you also have to look at the L1,L2 and L3 cache. Some dual core cpus do share L3 cache and this affect the performance as well. Normally AMD 64bit cpu have greater cpu clock than Intel. It is hard to compare the cpu performance base on CPU architecture. There are few items that contribute to the overall performance such as cpu interconnect architecture, Message Passing Interface and network connection (for cluster). The best is to do the benchmarking for different hardware vendor.

Steve August 15, 2006 07:22

Re: How many licenses for dual core processors?
Nobody seems to have answered the thread's title question. You'll need one license per STAR-CD process, regardless of whether they are on the same host, serial, parallel or whatever. There's no way to use your resources more cost effectively by careful choice of architecture. Some codes allow license sharing for the same user/host/display. Not STAR-CD though.

TG August 15, 2006 08:12

Re: How many licenses for dual core processors?
You really aren't telling the whole story. You need 1 starsuite license to kickoff any STAR analysis and 1 star-hpc license for each additional parallel process. star-hpc licenses are significantly cheaper than starsuites. So it is more effective from a cost standpoint to run 1 job split 4 ways (and get the answer 4x quicker) than it is to run 4 serial jobs at the same time. The cost structure encourages users to use parallel processors because star-hpc licenses are so much cheaper than a starsuite.

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