AMD's Quad FX: Technically Quad Core
by Anand Lal Shimpi on November 30, 2006 1:16 PM EST- Posted in
- CPUs
More Sockets, but Lower Performance?
When AMD briefed us on Quad FX, the performance focus was on heavy multitasking (AMD calls this "Megatasking") or very multi-threaded tests. We figured it was an innocent attempt to make sure we didn't run a bunch of single threaded benchmarks on Quad FX and proclaim it a failure. Given that the vast majority of our CPU test suite is multi-threaded to begin with, we didn't think there would be any problems showcasing where four cores is better than two, much like we did in our Kentsfield review.
However when running our SYSMark 2004SE tests we encountered a situation that didn't make total sense to us at first, and somewhat explained AMD's desire for us to strongly focus on megatasking/multithreaded tests. If we pulled one of the CPUs out of the Quad FX system, we actually got higher performance in SYSMark than with both CPUs in place. In other words, four cores was slower than two.
| CPU | SYSMark 2004SE | Internet Content Creation | Office Productivity |
| 2 Sockets (4 cores) | 261 | 373 | 182 |
| 1 Socket (2 cores) | 288 | 393 | 211 |
You'll see that in some of the individual tests there is an advantage to having both CPUs installed, but in the vast majority of them performance goes down with four cores. It turns out that there are two explanations for the anomaly.
| CPU | Internet Content Creation | 3D Creation | 2D Creation | Web Publication |
| 2 Sockets (4 cores) | 373 | 245 | 514 | 411 |
| 1 Socket (2 cores) | 393 | 364 | 453 | 369 |
First, in Internet Content Creation SYSMark 2004SE, there appears to be an issue with having two physical CPUs in the system that results in the 3dsmax rendering test only spawning a single thread, lowering performance below that of a normal dual-core processor. This problem may be caused by a licensing violation within the benchmark where it is expecting to see one physical CPU with multiple cores and isn't prepared to deal with multiple CPUs. Regardless of the exact cause of the problem, it doesn't appear to be anything more than a benchmark issue. It's the performance in the Office Productivity suite that is far more worrisome because there is no issue with the benchmark that's causing the problem.
| CPU | Office Productivity | Communication | Document Creation | Data Analysis |
| 2 Sockets (4 cores) | 182 | 171 | 259 | 137 |
| 1 Socket (2 cores) | 211 | 187 | 285 | 176 |
The Office Productivity suite of SYSMark 2004SE wasn't the only situation where we saw lower performance on Quad FX than with a single dual core setup. 3D games seemed to suffer the most; take a look at what happens in our Oblivion and Half Life 2: Episode One tests:
| CPU | Oblivion - Bruma | Oblivion - Dungeon | Half Life 2: Episode One |
| 2 Sockets (4 cores) | 67.3 | 78.3 | 155.8 |
| 1 Socket (2 cores) | 75.2 | 90.9 | 165.7 |
Once again, populate both sockets in the Quad FX system and performance goes down. The explanation for these anomalies lies in the result of one more benchmark, CPU-Z's memory latency test:
| CPU | CPU-Z Latency (8192KB, 128-byte) |
| 2 Sockets (4 cores) | 55.3 ns |
| 1 Socket (2 cores) | 43.3 ns |
With both sockets populated, memory latency goes up by around 27% and thus in applications that are more latency sensitive and don't necessarily need all four cores, you get worse performance than with a single dual-core CPU. The added latency comes from the additional probing over the HT bus that's done for coherency whenever a memory request is made to see where the latest copy of the data resides.
It's a problem that will go away if you have a single quad-core CPU with one memory controller, but one that makes Quad FX a tougher pill to swallow compared to Intel's quad-core offerings.
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JarredWalton - Thursday, November 30, 2006 - link
Why is it that just putting the other 2 cores on the same package reduces power consumption so much?It doesn't. Core 2 Duo uses less power than Athlon FX-62, so two of them are going to use less than two FX-62 (or whatever) chips. Now, adding the second socket also adds additional voltage regulation circuitry, so the second socket will increase the power load, but I don't think the second socket accounts for more than a 20W power increase, and probably more like 10W.
Slaimus - Thursday, November 30, 2006 - link
The odd thing for this platform is that the single CPU is actually really cheap versus comparable products. If only server boards can take these CPUs.Beachboy - Thursday, November 30, 2006 - link
I wonder how many diehard AMD enthusiats will want to split a set of these "quads".mino - Friday, December 1, 2006 - link
Count me in!IMHO enthusiast forums are will be full of guys sharing the CPU purchase... :)
peternelson - Friday, December 1, 2006 - link
Very likely eg I would and thought of that, knowing the guys on forums I frequent ;-)The other option is just buy two motherboard/systems and put each of the paired cpus into each one.
rqle - Thursday, November 30, 2006 - link
Best case scenario.100% price reduction in mainboard
Assume these FX cpu perform as well as QCore
Price it Similar to Performance
Major Power Reduction
Assume it a windows error =/ , no clue why you would run server software and e-commerce over softwares/games on this platform
I still have a very hard time recommended this setup to an enthusiast. Already have a hard time reaching 3.0ghz, it going to have a very hard time going just 10% beyond that. The upper limit of AMD cpu doesn’t impress me right now. Cheapo Intel Core 2, with an overclocker in mind seem to have more potential.
photoguy99 - Thursday, November 30, 2006 - link
I generally agree with your logic -But even your best case scenario is impossible because two 90 process CPUs have never come close to the power comsumption of a single 65 process CPU at the same performance.
mino - Friday, December 1, 2006 - link
Depends. EE X2's are more efficient than C2D's. Even performance wise.Not even comparing IDLE C'n'Q and EIST enabled ....
Anonymous Freak - Thursday, November 30, 2006 - link
Of course they'll sell more FX processors now than before. There was literally nothing to differentiate them before, other than clock speed. That, plus now they'll sell two for every computer built with them.But, I have a feeling that the FX processors are going to be even more niche than they were before. Before, it was at least a high end normal processor. Someone could buy a midrange system, and upgrade to an FX later. Now, you have to decide up front that you're going to pay a fortune for the computer. Presently, I have an el-cheapo $99 motherboard that I put my old Pentium 4 in. If I want, I can slap a Quad-Core Core 2 Extreme in there. I can't do that with AMD's setup.
I'm not an Intel fanboy, either. The only reason I even have the Pentium 4 is because a friend gave it to me free when he upgraded his system. I was perfectly happy with my laptop and my AthlonXP 1700+. But a free 3.8 GHz processor is a free 3.8 GHz processor. I went and bought the cheapest motherboard and memory I could find. Spent about $200, and I can upgrade to quad core anytime I want. (Although I'll probably upgrade from the onboard video to a decent PCI-E card first.)
photoguy99 - Thursday, November 30, 2006 - link
I don't know man, why would they sell any more?
To sell more someone would have to buy this "Ford Excursion" of a system. But who is going to buy this?
What boutique shop is going to even sell it?
Is there one single person here who is planning to get one?