Thursday, October 18th, 2007

Using FSX with SLI and multi-core processors… does it work?

The first stage of this project will focus on building a computer to run FSX. So far as gaming goes FSX is probably one of, if not the most, demanding programs currently on the market. I mean think about it, the software contains a 3D dynamic simulation of the entire world whilst also simulating the systems and physics of an airplane, traffic, ATC… all in high-resolution graphics. Not surprisingly, many people report struggling to run the software on their own systems.

Some have been very critical of this, saying that Microsoft shouldn’t release software which perhaps (although I am to test this myself) can’t be run at full power on any reasonable consumer computer. I, however, share a different view. I think it’s good for the software manufacturers to test the limits of current hardware. Specifically with FSX, one can always turn down the settings to achieve better performance. But more importantly, I think it’s great that designers are building software that demands state-of-the-art computing technology. There isn’t much point in investing in a top-end high-performance gaming computer if the software isn’t going to test the limits of the hardware!

Anyway enough of that and onto some specifics. My first area of research for building my FSX computer (as I’m calling it) is how well FSX works with Scalable Link Interface (SLI) video card technology and multi-core processors. In short, is it worth investing more project money in these additional technologies or would such an investment just be wasted money? If you’re not familiar with SLI and multi-core processors here is the super-quick summary:


SLI
SLI basically means that you can use two separate video cards, and hence graphics processing units (GPUs), to run one display. This is a way of achieving tomorrow’s performance today by sharing the computing load for a single display across two cards. Most general benchmarking studies report the ability to nearly double the graphics performance using such an approach. There are some technical details that one has to consider when building an SLI system, but we’ll get into that a lot more later in the project.


Multi-Core Processors
Multi-core processors follow a somewhat similar approach with the CPU. Up until about 18 months ago, most consumer processors were ‘single threaded.’ This basically means the processor can only perform one task at a time. Think of it as one person at a desk with one ‘In’ tray processing each piece of incoming paperwork one at a time. Multi-core CPUs, however, essentially contain several processors on a single chip. The first versions contained two ‘cores’, four ‘cores’ are now available and in the future we’ll see many more. This setup allows the CPU to perform several tasks at the same time. Think of this as two people sitting at a desk processing the paperwork from the ‘In’ tray. One person processes all of the red forms and the other person processing all of the blue forms. As a result, the whole pile of paperwork gets processed much faster. You can see why this is such a big deal since, as with SLI, it’s a way of processing information much faster without actually physically running the processor any faster (in terms of cycles-per-second, e.g. 3.0 GHz).

Now, how does all of this stuff relate to FSX?
Well there have been many conflicting reports out the as to whether FSX ‘works’ with SLI and multi-core systems. I spent a while researching all of the facts and here’s what I found:

Does FSX ‘work’ with SLI?
Yes. In fact all programs ‘work’ with SLI. For the most part (when you have a separate graphics card and not ‘integrated graphics’ via your CPU) the process of actually drawing and creating the images on your screen is separate from other processes associated with the computer. FSX, or any other software, essentially phones up the graphics card and says ‘hey, draw this on the screen’ and the graphics card then takes care of the rest of the process. All of the technology associated with SLI occurs within this separate process associated with the graphics cards. For all essential purposes, FSX doesn’t really need to know what’s going on with the graphics processors.

But don’t some people report that they use SLI with FSX and don’t see much improvement?
Yes, there are many reports out there about this. However, as mentioned above the SLI process is separate from the program being run and so all software ‘works’ with SLI. The reported lack of performance improvements when using SLI with FSX doesn’t have much to do with the graphics cards and is instead primarily a limitation of the CPU. Essentially, the SLI graphics cards are having no trouble drawing what’s being displayed on the screen, RATHER, the CPU is getting caught up and not able to send out ‘go draw this’ orders fast enough.

But I thought all one needed was a kick-ass graphics card and all is fine?
Quite often for many games this is the case. If you spend all your money on the graphics card and then only have a so-so CPU you’ll still get excellent performance. For many games it’s the process of drawing the graphics that is the ‘most demanding’ part of the program. However, FSX is a bit different. There are certainly amazing graphics to draw but the program is also doing so much more including simulating traffic, ATC, aircraft systems, physics and so on. All of this takes up precious CPU time and as a result, on many systems, the CPU ends up being the limiting factor in performance.

Shouldn’t multi-core processors help this?
Yes, but at first they didn’t. Many people were reporting that FSX was only using one of their processors cores and this was indeed the case. The original release of FSX was not programmed to utilize multi-core processors. The software needs to be programmed to divide up separate processes and assign them to separate processor cores. Consequently, for those with multi-core processors, FSX was essentially only utilizing a small percentage of the CPU’s true power. Fortunately, this issue was addressed in FSX Service Pack 1 to allow for full-utilization of multi-core processors thus resulting in a big performance boost for many users.

So what’s the take-home message?
Well the whole point of checking all of this out was to get some initial ideas about what parts of the computer I should invest more money in. I too was often of the previous mindset that one should focus on the graphics cards and that should take care of most of the problem. However, with FSX it would seem that is a big mistake. Instead it seems the only way to achieve the best performance is to pair up a top-of-the-line CPU with top-of-the-line SLI graphics cards. If you go for the best graphics cards and then get a slightly cheaper CPU you’re only shooting yourself in the foot since the graphic cards will never be able to rev up to full power as the CPU will be limiting the process. At current prices, this would mean spending about $2,000 on the GPUs and CPUs (2/3 of my budget goal of $3,000 for the computer) so stay tuned to see how it all plays out!

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7 Comments on “Using FSX with SLI and multi-core processors… does it work?”

  1. Bob Vertalics Sr

    Hi! I enjoyed your comments, but (you knew there would be a BUT in there somewhere) I have a AMD X2 6400 3.2ghz with 4 gb Mem, 1100 watt PSU, Asus M2N32 SLI mobo and 2 9800 GX2’s. I have found “NO” performance improvement going from 1 card to 2 cards in quad SLI … Also I was running 2 8800 GTS’s and again “NO” performance improvements going to SLI … Many of the forums I have gone to report the same…. Code guys say FSX does not support SLI

  2. Stu Frost

    I saw a loss of performanse that was unbelievable. Using only one 8800GTX I saw FPS at the most complex views at 30-45. When I used the SLI technology, the FPS dropped to 3-5 FPS at the same location and conditions. What a waste to have purchased the second video card.

  3. Mike Davis

    There is an excellent article in the recent issue of Computer Pilot magazine (Jan 2009) by Doug Horton in which he compares CPU vs. GPU and their effect on FSX framerates. Four nVidia cards were tested (7800 GT o/c, 8800 GT, 9800 GTX and GTX 260) and a quad core CPU clocked (and overclocked) at 2.4, 2.7 and 3.0GHz. In short, what he found is that the graphics cards (except the older 7800) had almost no effect on framerates, but the CPU speed increased framerates in an almost perfectly linear fashion.

    In other words, FSX is CPU dependent for framerates provided you have a video card at least as good as an 8800 GT or better. SLI does not help. Microsoft (and P.T. Taylor) has been telling us this for a long time.


  4. Thanks for the info Mike.

    I would certainly agree that the extra video card with SLI does not have much impact on graphics performance.

    I wouldn’t say I regret adding the second card to my system (as it does help for some other games), but for FSX I don’t think it’s necessary. When budgeting for a new computer for FSX I would say save the money on SLI and invest it into the best processor you can afford.

  5. Troi

    I have decided to build a FSX specific machine. I am looking at getting he fastest dual processor and over-clocking it as high as will will go and still be stable. But, I am open to purchasing a quad-processor. I have FSX with SP2. Have any of you heard whether the the performance increase in FPS of a quad is really that much better than the fastest overclocked dual processor? I have a saying: “If you cannot see the difference, why pay the difference?” So, is speed difference between a quad processor over a dual that much better? Thanks again guys, as I have learned much in reading these posts.

  6. Darrick

    I recently built a new “budget” rig with a mind to improve FSX frame rates. This is what I came up with:

    MOBO…….. Gigabyte EP45T-UD3LR
    GFX……… Saphire HD4870 vapor-x 2 gig
    CPU……… Intel Q9550
    RAM……… Crucial Ballistix 2x2gig DDR3 1333
    CASE…….. Antec Sonata Designer 500 (w/500 watt power supply)
    CPU Cooler.. Cooler Master Hyper 212

    Overclocked cpu to 8.5 x 418 = 3553ghz
    Runs stable and cool 32/idle 58/full load prime 95
    Runs at 3.8ghz but throttles back to 2 cores w/o upping voltage.
    Memory at 1338mhz w/6-6-6-20 timings.
    Running Windows 7rc 64 bit.

    Now on to FSX…. Can run all settings maxed but fps drops below 20fps at times (can view fps by hitting shift + z twice). By monitoring cpu load I can see all 4 cores maxed most of the time, so FSX is very cpu dependent. By backing off Auto Gen Scenery a bit It runs at a comfortable 30+ FPS at 1680×1050 res. (max for my 22″ lcd). I think this combination is good and the GPU and CPU are getting maxed out about the same time.

    If I were to make adjustments to the above build I would use the Gigabyte EP45-UD3P board….. more expensive but crossfire ready and uses DDR2 memory (DDR3 is too expensive and not in its prime yet). You should get an easy 3.7 to 4.0 ghz on this set up. Also would go with HD4890 1 gig series or gtx 260/275 series and be able to crossfire another card at a later date.

    Note: I was able to buy all the parts incl. shipping for less than $750.00 by waiting for good deals to come along. Used ewiz.com, newegg.com, amazon.com.

    P.S. the cpu cooler and fan assy are big and they get mounted to the MOBO while out of the case. Ok for a new build but a real pain just to upgrade a cpu cooler.


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