Print 112 comment(s) - last by MrPoletski.. on Jan 27 at 11:45 AM

Sandia simulations reveal memory is the bottleneck for some multi-core processors

Years ago, the hallmark of processor performance was clock speed. As chipmakers hit the wall on how far they could push clock speeds processor designs started to go to multiple cores to increase performance. However, as many users can tell you performance doesn't always increase the more cores you add to a system.

Benchmarkers know that a quad core processor often offers less performance than a similarly clocked dual-core processor for some uses. The reason for this phenomenon according to Sandia is one of memory availability. Supercomputers have tried to increase performance by moving to multiple core processors, just as the world of consumer processors has done.

The Sandia team has found that simply increasing the number of cores in a processor doesn't always improve performance, and at a point the performance actually decreases. Sandia simulations have shown that moving from dual core to four core processors offers a significant increase in performance. However, the team has found that moving from four cores to eight cores offers an insignificant performance gain. When you move from eight cores to 16 cores, the performance actually drops.

Sandia team members used simulations with algorithms for deriving knowledge form large data sets for their tests. The team found that when you moved to 16 cores the performance of the system was barely as good as the performance seen with dual-cores.

The problem according to the team is the lack of memory bandwidth along with fighting between the cores over the available memory bus of each processor. The team uses a supermarket analogy to better explain the problem. If two clerks check out your purchases, the process goes faster, add four clerks and things are even quicker.

However, if you add eight clerks or 16 clerks it becomes a problem to not only get your items to each clerk, but the clerks can get in each other's way leading to slower performance than using less clerks provides. Team member Arun Rodrigues said in a statement, "To some extent, it is pointing out the obvious — many of our applications have been memory-bandwidth-limited even on a single core. However, it is not an issue to which industry has a known solution, and the problem is often ignored."

James Peery, director of Sandia's Computations, Computers, Information, and Mathematics Center said, "The difficulty is contention among modules. The cores are all asking for memory through the same pipe. It's like having one, two, four, or eight people all talking to you at the same time, saying, 'I want this information.' Then they have to wait until the answer to their request comes back. This causes delays."

The researchers say that today there are memory systems available that offer dramatically improved memory performance over what was available a year ago, but the underlying fundamental memory problem remains.

Sandia and the ORNL are working together on a project that is intended to pave the way for exaflop supercomputing. The ORNL currently has the fastest supercomputer in the world, called the Jaguar, which was the first supercomputer to break the sustained petaflop barrier.

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RE: 2x4
By Uncle on 1/18/2009 1:14:21 PM , Rating: 2
You changed your whole system out, you should have bought the 9800gtx and tried it before some one advised you to buy a new system. I'm sure Crysis would have played fine. I'm getting the idea that you now have to justify your purchase.

RE: 2x4
By RubberJohnny on 1/18/2009 8:40:19 PM , Rating: 2
Maybe YOU should have tried a new CPU before telling everyone that upgrading is a waste of money???

I recently went from an OC'd 939 4200x2 to a Q6600 (stock ATM, stuck with the same 4850 vid card) and the performance increase was MASSIVE. My FPS increased dramatically and the whole experience is just so much smoother - RTS were the biggest improvement! Not sure how this would compare to a really fast core 2 duo but i needed the extra cores for virtualisation.

My recent upgrade cycle has gone 4200x2+7900gs --> 4200x2+4850 --> q6600+4850 and i can tell you the biggest jump in performance was the CPU not the vid card and I game at 1920x1200.

So i'm calling SHENADIGANS on uncle...time to upgrade son!

RE: 2x4
By Uncle on 1/18/2009 9:42:37 PM , Rating: 2
Big difference between an 4200x2 vs opteron 165.

RE: 2x4
By RubberJohnny on 1/18/2009 10:43:15 PM , Rating: 2
Yeah and there's an even bigger difference between an opty 165 and a Q6600 which is exactly my point...

RE: 2x4
By SlyNine on 1/18/2009 11:55:18 PM , Rating: 2
Mean while the 4850 is around 8x faster then your 7900GS.

In games since they only really use 2 cores right now your Q6600 is about equal to a opty at 3ghz. My friend I have run many benchmarks with the A64 x2 and Q6600.

You are dead wrong.

RE: 2x4
By Denithor on 1/19/09, Rating: 0
RE: 2x4
By SlyNine on 1/19/2009 11:43:29 PM , Rating: 2
First off core per core the E8500 is better then the Q6600, Second off I benchmarked both the Q6600 and 4200X2 at stock and overclocked speeds . At 2.4 ghz the Q6600 does not score hardly any more FPS then a 4200X2 at 3Ghz in games that do not support good SMT.

I didn't say any thing about gaming on a single core, But I can tell you assassins creed isn't even playable on a single core.

SupCom may get higher FPS and have a smoother interface w/quad, but suffers from the same simulation slow down at 2.4 ghz as a 4200X2 @ 3.0ghz. Supreme Commander does not support Quad core's with a crap unfortunately because right now it's my favorite game.

UT3 is good and I have yet to try GTA4.

With a Q6600 stock I've seen maybe a 2% increase in FPS from my old A64 at 3.0ghz. an e8500 is probably a bit better. But still not night at day in games, This isn't sisoft sandra were talking about.

Moving forward yes, the Q6600 is a better future investment then any dual core.

RE: 2x4
By mindless1 on 1/21/2009 4:57:42 PM , Rating: 2
Why would anyone use a turd like GTA4 as an example?

Bottom line - You don't need more than 3GHz from a dual core processor to play most modern games fine, providing the video card is also up to snuff.

A single core at 3GHz is also viable for over 50% of the games out there today. It may not win the benchmark graphing contest, but it will maintain a playable framerate at enough games. Will it play the extra demanding ones well? Consider the question before answering, benchmarks and reviewers deliberately try to find something to show contrast, instead of the typical games that will run fine on most of the hardware tested!

Truth is, yes someone with a single core Athlon 64 who upgraded their video a couple times has had a great value run at gaming. They may not be able to extend this much into the future, but as always we can't ever think any gaming combo will last far into the future until the future is here.

Any game that won't run properly on a $60 CPU is defective. That's what the eyecandy adjustment settings are for, but in the end those make not much difference in gameplay enjoyment compared to the eyecandy settings related to GPU performance and resolutions possible at playable framerate.

It always was and still is more about the video card than anything else. Moreso than ever today with monitors continuing to rise in resolution.

RE: 2x4
By SlyNine on 1/18/2009 11:52:39 PM , Rating: 2
You ever check out your CPU load on these games. It almost never hits 100% on any core if you are not running a 8800GT or better.

I had a 4200X2 939 for some time and also upgraded to the Q6600. Ran the 4200x2 with a 1900XT and then upgraded to 8800GT, Then upgraded to a Q6600 and got my other 8800GT card after a time.

The biggest performance increase by FAR was going to the 8800GT on the 4200X2, the second biggest was adding another 8800GT. The Q6600 upgrade was nice, but not nearly the jump.

The 1900XT>7900GS , the 4850>8800GT. You had an even bigger jump in video and yet say the CPU was your biggest jump. You sir are full of poop. Or you are running all your games at 1024x768 with no AA.

RE: 2x4
By RubberJohnny on 1/19/2009 7:11:04 AM , Rating: 2
What res were you running? CPU load on the games i mostly play - TF2, BF2 and Company of heroes were maxing out some of the time at 1920x1200 with the X2 4200+ (BF2 1600x1200). When i turned off AA things did not really get any smoother so it must have been the cpu holding the 4850 back. Things didn't get acceptably smooth till i lowered the res back to 1280x1024.

However when i got the Q6600 i could run all of those games on full quality at 1920x1200 and they were sliky smooth (ok maybe COH isn't silky on full ;) Perhaps my X2 4200+ system had some other hardware issue (was a clean xp build) but i always felt that 4850 didn't perform like i expected till i paired it with the Q6600.

RE: 2x4
By SlyNine on 1/19/2009 11:53:10 PM , Rating: 2
Well, Im going to eat alittle crow, I have not played or tested those games,

I play FC2, Crysis, Americas army, SupCom ( supreme commander), Gears of war(big improvment going to the Q6600), Grid, and Stalker.

But still in all my games the biggest improvment was going to the better video card, perhaps you were having some other problem that was fixed with your Q6600 setup.

You have a much better setup moving forward then you did with the 4200x2 so no need to worry.

RE: 2x4
By MrPoletski on 1/23/2009 4:43:39 AM , Rating: 1
i7@3.7Ghz here, wouldn't go back if you paid me.

There is something sektheh about 8 individual performance bars in task manager;) yes I know there are only 4 processors.

SERIOUSLY though, I think a slight change should be made in relatio to perating systems and CPU's. You operating system has a task handler, that decides what processor gets used by what apps and such.

Well I think that job would be better done by an arbiter on the CPU itself, that makes the chip appear as a single core and divides the workload amongst its loyal servant cores.

Would make coding for multicore systems a lot easier.

RE: 2x4
By MrPoletski on 1/27/2009 11:45:18 AM , Rating: 2
Nobody like the idea of hardware task management?

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