Re: no. of CPUs for optimal GTX-690 performance

From: Michael Purdy (
Date: Wed Nov 07 2012 - 08:45:13 CST

Thanks everyone for the input. A clarification on my original post, the
current Opterons are 2200 series (dual core) and the GTX-690 is plugged
into a PCIe 2.0 slot.

So increasing the CPU clock speed here is what I'm considering:

Dual Xeon E5-2670 Sandy Bridge-EP 2.6 GHz (8-core) CPUs
GTX-690 (2 GPU, 3072-core)
Asus Z9PE-D8 WS motherboard

motherboard specs
Intel® Socket 2011 Processors
Dual Intel® Xeon® processor E5-2600 product family
Supports Intel® Turbo Boost Technology 2.0
Chipset Intel® C602
Memory 8 x DIMM, Max. 64GB, DDR3
2133(O.C.)/2000(O.C.)/1866(O.C.)/1600/1333/1066 MHz ECC, Non-ECC,
Un-buffered Memory
Quad Channel Memory Architecture
System Bus 8.0/7.2/6.4 GT/s Intel® QuickPath Interconnect
Multi-GPU Support Supports NVIDIA® 4-Way SLI™ Technology
Supports AMD Quad-GPU CrossFireX™ Technology

The total cost of this workstation will be about $5000 ($3079 for the
CPUs). Has anyone tried the AMD FX-8350 Vishera 4.0GHz (8-core) $219?


On 11/07/2012 05:34 AM, Ajasja Ljubetič wrote:
> Can't find the benchmarks right now, but if I remember
> correctly, hyper-threading was not much use. Under linux, there was no
> speedup when using 8 instead of 4 threads (either with or without the
> GPU). Under windows there was about 5-10% gain when using hyper
> threading.
> I think Giacomo's advice is very sound: I'd go for higher clock speeds
> as well.
> Best regards,
> Ajasja
> On 6 November 2012 21:46, Giacomo Fiorin <
> <>> wrote:
> One additional thing that complicates things for Sandy Bridge
> processors is the Turbo Boost. You had equal speed between 4
> cores and 7 cores, so things were not going so well. Many people
> have dealt with this problem for benchmarking purposes, and posted
> different solutions online to disable it. (Ajasja: how are your
> scalings without GPU?)
> In any case, the main problem is most often the limited bandwidth
> between CPU and GPU, like Ajasja and Aron already said. The
> motherboard that you're planning to use is a good choice, the one
> you're currently making tests on may not be: what is it?.
> Also not knowing which Opterons you had nor the PCI-e bus
> speed, the comparison you made with the ThinkPad is not informative.
> That said, I don't think it's worth going beyond 1 CPU for every
> GPU. First, it will be hard to find suitable motherboards.
> Second and most important, 12-16 CPU cores plus 2 GPUs all
> exchanging data on the same bus will probably already clog up the
> PCI-e bus. I agree with Ajasja that hyperthreading may be
> useless, and actually harmful if you're sharing the bandwidth
> (that would be 24-32 CPU cores.. again all sharing the same bus).
> On which CPU, I would vote for less cores but higher clock (e.g.
> Xeon 2640 or 2667), if you're planning to use them with a GPU.
> Giacomo
> On Tue, Nov 6, 2012 at 2:01 PM, Michael Purdy <
> <>> wrote:
> Hello, I am running NAMD simulations (multicore-CUDA) on a
> ThinkPad with dual Core i7-2760QM CPUs and a Quadro 2000M
> running Debian. For a 150k atom system I get performance like
> this:
> Benchmark time: 4 CPUs 0.287062 s/step 1.66124 days/ns 387.641
> MB memory
> Benchmark time: 7 CPUs 0.289229 s/step 1.67378 days/ns 428.574
> MB memory
> Things are going well so we purchased a GTX-690 which we
> installed in a workstation with two dual core Opterons, which
> is evidently far short of the CPU cores we need to get the
> most of the 2 GPUs and 3072 cuda cores. Performance was just
> slightly better than the ThinkPad:
> Benchmark time: 4 CPUs ~0.2 s/step ~1.4 days/ns
> We would like to build a new workstation to get the most out
> of the GTX-690 and I'd like to know how many CPU cores we
> need. I'm considering two Core i7-3930k (6-core/12-thread) or
> two Xeon E5-2650 (8-core/16-thread). Will either of these be a
> good match for the GTX-690 or will I still be short running
> short on CPUs? The current plans is to build this on an Asus
> Z9PE-D8 WS board.
> Michael

Michael Purdy
University of Virginia
480 Ray C. Hunt Dr., Rm 320
Charlottesville, VA 22903

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