where's the drop off with multi core cpu's?

[boing]

i'm putting a system together for use with Max (3d modelling software) which benefits greatly from multi-core cpu's. I was curious, with the potential for octo core systems is there a point where the FSB or memory just cant supply all the cores? is there a natural bottleneck ata level that there's no point going beyond? I don't want to go mental if it isn't going to produce substantial results.

 

[Roguestar]

The current 8-core system is two 4-core CPUs, both with their own FSB. It seems that one FSB per 4 cores seems as high as Intel is willing to take that ratio at the moment, with current memory controller architecture. I wouldn't say there's a natural limitation as such, as FSB/HTT/memory controller/whatever interfaces are always going to have less bandwidth than on-die communication but as long as they can saturate the RAM there's not that much to worry about. I think currently we're not seeing FSB saturation having too big an impact with quad-core CPUs doing stuff like rendering, just that the other cores aren't as well put to use in a lot of programs that claim multi-CPU scaling. On that note, if it's the kind of software that'll run on an 8-way server then it's well threaded and you shouldn't have too much bother. To be honest, overall, we don't really know yet. Average Joe does not own a quad-core CPU and even Steven Gamer only has a quad-core if he's at the bleeding edge (the blood comes from the wallet!) so there are very very few people who'd use an 8-core desktop PC. There'll come a point where you have to say "this job is too big for one [desktop] PC" and split it up or run it on something bigger or dedicated.

In short: "Hmm, hah? Hum."

 

[boing]

if i didn't opt for an 8 core system my laymans logic suggests a twin socket motherboard with dual core would outperform a single socket board with quad core. would that seem sensible?

 

[Boyo]

For now, I would just stick with dual core.

 

[boing]

is it possible to use multiple core 2 duo on a twin socket board or is that purely a xeon thing?

 

[Matthias99]

Originally posted by: boing
is it possible to use multiple core 2 duo on a twin socket board or is that purely a xeon thing?

I believe you need Xeons for multi-socket operation. At least that's the way it has always worked previously.

You can definitely reach a point with memory-bandwidth-limited applications where more CPU power will not help you. I think AT (or maybe THG? Or both?) had some articles on scaling of Opteron 8XXs versus P4-based Xeon MPs in multi-CPU server configs when the Opterons were coming out. Because they had a memory controller per CPU and weren't being throttled by the FSB like the Xeon MPs, they scaled a lot better with some workloads.

IIRC, at the time it seemed like more than 4 cores was too much for one dual-channel DDR400 memory interface to keep fed, as the Pentiums fell off badly in 8-way configs. Of course, it depends greatly on the workload.