GPU Performance vs. CPU Clock Speed

For these tests, we took a single core AMD Athlon 64 (1MB L2) and increased its clock speed from 1.8GHz all the way up to 2.6GHz, measuring performance at each step of the way. The image quality settings haven't changed; what we're looking for here is if there's a pattern in the CPU/GPU relationship.

We picked four GPUs to look at their CPU dependency: the Radeon X1900 XT CrossFire, X1900 XT, X1800 XT and X1800 XL. We chose these four configurations because they represent the best ultra high end, high end, upper mid-range and mid-range GPUs for Oblivion. Our main interest is in finding out if there is a point at which the best mid-range GPU ends up being faster than the best high end GPU because of being paired with a faster CPU, or if having a faster GPU is really all that matters in Oblivion.

What this graph proves is that our Oblivion Gate benchmark is really only CPU bound if you've got a pair of X1900 XTs in CrossFire. What this does mean is that if you've got a low end Athlon 64, you won't see much of a performance difference between a single X1900 XT and a pair of them running in CrossFire mode. But for the most part this benchmark is no different than what we've seen from other games, with the X1900 XT, X1800 XT and X1800 XL being basically GPU bound - let's see if our other two tests show the same picture.

The Town benchmark is extremely CPU bound as you can see by this graph, and in Oblivion you do spend quite a bit of time walking around in towns. Being able to isolate the individual lines in this graph isn't very important because they basically all show the same thing, but what is important is to be able to look at the graph two dimensionally. What this graph shows us is that a single X1800 XT paired with a 2.4GHz CPU offers much better performance than an X1900 XT with a 1.8GHz Athlon 64, thus stressing the need to have a balanced CPU and GPU setup in order to avoid wasting money on a fast GPU. We already saw in our GPU performance article that CrossFire (and SLI) do nothing for performance in our Town/Dungeon benchmarks so the behavior here is not surprising.

Much to our surprise, the Dungeon benchmark ended up being a lot more GPU bound than the Town test but the conclusions we can draw are very similar. The Radeon X1800 XT does extremely well when paired with a high end CPU and will actually offer the same performance as a Radeon X1900 XT with a lower end or mid range CPU; it isn't until you give the X1900 XT a faster CPU as well that it can really stretch its legs and offer the performance advantage we know it has over its predecessor.

Oblivion CPU Performance Hyper-Threading and SMP Tweaks
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  • goku - Saturday, April 29, 2006 - link

    It' really ticks me off that oblivion couldn't incorporate support for the new ageia physics processor. It would have been nice to see all those calculations being offloaded onto the PPU instead so that the CPU wouldn't have such an effect on performance.
  • DigitalFreak - Saturday, April 29, 2006 - link

    Since they are using the Havock physics engine, it was never going to happen.
  • DigitalFreak - Saturday, April 29, 2006 - link

    Oops, Havok
  • Madellga - Saturday, April 29, 2006 - link

    I don't think that was supposed to happen, but when I clicked on the link under the tittle:

    SMP - enhacing performance , it goes to http://www.anandtech.com/printarticle.aspx?i=2747">http://www.anandtech.com/printarticle.aspx?i=2747 , which is the same Oblivion CPU article we are reading.

    I think the idea is to take us to the guide you are using, isn't it?

    //s
  • kristof007 - Saturday, April 29, 2006 - link

    Same here. Please fix it Anand when you get a chance.
  • JarredWalton - Saturday, April 29, 2006 - link

    Done. That page was my doing - Anand ran the tests, I wrote page 5. I forgot to paste in the link. (Actually, I ran into some issues with undo/redo and apparently lost the link in the process. I had to rewrite two paragraphs at the time.)

    Jarred Walton
    Hardware Editor
    AnandTech.com
  • shortylickens - Friday, April 28, 2006 - link

    This makes me feel pretty good. I went out of my way to get the cheapest Socket 939 CPU I could find.
    Now that I've had the system for a while, I feel OK about doing one big CPU upgrade and I can actually see a performance boost.
  • bloc - Friday, April 28, 2006 - link

    The sempron line is amd's answer to intels celeron line.

    Might it be possible to see the benches for the Sempron S754 as they're budget cpu's with huge overclocks?
  • kmmatney - Saturday, April 29, 2006 - link

    A Sempron 2800+ overclocked to 2.4 GHz performs about the same as an Athlon 64 3700+ clocked at 2.2 GHz. So for a rough estimate, lower the Athlon64 speed by 10% to get the speed of a Sempron.

    My Sempron overclock at 2.45 Ghz was 100% stable for all games and applications I'd ever used until Oblivion. With Oblivion, the game was crashing until a lowered the spu speed to 2.35 GHz.
  • JarredWalton - Saturday, April 29, 2006 - link

    Part of the problem is that there's only one SLI motherboard for socket 754, and honestly I think that's more of a novelty product than something truly useful. Anyone spending the money on multiple GPUs is better off buying a faster processor as well.

    Anyway, looking at how cache seems to affect performance of the other chips, I would guess that a Sempron 128K/256K would be equivalent to an Athlon 64 512K running 200 to 400 MHz slower. (i.e., Athlon 64 2.0 GHz -- 3200+ -- would probably be about equal to a Sempron 2.3-2.4 GHz.) Single channel memory plus a reduction in cache size should cause a moderate performance hit, clock for clock.

    Of course, none of that means that Sempron chips aren't worth considering, especially with overclocking. Assuming you're not running super high end graphics configurations, though, you can probably reached the point where you're GPU limited to the same performance, whether you have an Athlon X2 or a Sempron.

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