FX Vs. Core i7: Exploring CPU Bottlenecks And AMD CrossFire

References
By Thomas Soderstrom
published

AMD and Intel continue serving up increasingly faster CPUs. But graphics card performance is accelerating even faster. Is there still such a thing as processor-bound gaming? We take two Radeon HD 7970s, high-end desktop CPUs, and a few games to find out.

Battlefield 3, Frame By Frame

Though we usually talk about average frames per second, an even more important measure of playability is milliseconds per frame. That's because frames that take a relatively long time to render can be quite jarring. In theory, a 91 FPS rate could include a single 100-ms frame and ninety 10-ms frames, and that one 100-ms frame would be what kills your experience. 

This can happen on a single-GPU card. However, the complexities of synchronizing multiple GPUs make them more common in CrossFire and SLI configurations. We covered this micro-stutter effect in Micro-Stuttering And GPU Scaling In CrossFire And SLI, and have plans to cover this phenomenon in more depth in the next couple of months.

Since an evenly-spread 20 FPS rate would consist of 20 50-ms frames, we’re using 50 ms as the cut-off for actual playability in today’s analysis. Many gamers get annoyed with frame intervals far shorter (say, 30 ms), but that isn't as likely to get you killed as it is to simply bug you.

The performance of our Radeon HD 7970s in CrossFire appears fairly similar on our AMD- and Intel-based platforms when we run at 1920x1080. Our system based on the FX-8350 encounters a couple of higher spikes, but the worst of these we see only reaches up to 40 ms.

It's worth noting that we're using Fraps to take these measurements (currently the only solution, short of capturing the output with a PCI Express-based frame grabber). Consequently, we're not representing the entire rendering pipeline. After comparing our recorded results to actual gameplay, however, we're confident that the most egregious performance interruptions are being illustrated. Moreover, we're not comparing SLI to CrossFire, so the frame-time spikes are truly attributable to each platform.

Frame times simultaneously appear more variable (the bulk of the graph is wider) and with lower variability (the largest spikes are smaller) at 4800x900. Both platforms seldom cross the 30 ms barrier, and the AMD-based machine only spikes to 40 ms once.

You'll probably want to stop at 4800x900 or dial detail settings back to the Medium preset if 30-ms and greater frame times bother you. Ultra-quality details at this super-high resolution appear barely playable.

Thomas Soderstrom
Thomas Soderstrom
Thomas Soderstrom is a Senior Staff Editor at Tom's Hardware US. He tests and reviews cases, cooling, memory and motherboards.
164 Comments Comment from the forums
  • A Bad Day
    We were hoping that AMD's Piledriver update would break that trend, but even a handful of impressive advancements aren't enough to match the effectiveness of AMD's graphics team. Might Steamroller be the evolutionary step forward needed to unleash the GCN architecture's peak performance?

    I disagree. What's needed is even stronger push on the developers to use more than four cores, effectively, not some 100% load on one core and 10% on the other five cores.
    Reply
  • acktionhank
    Great article and very informative. The FX-8350 really held it's own until it came down to Skyrim.

    A Bad DayI disagree. What's needed is even stronger push on the developers to use more than four cores, effectively, not some 100% load on one core and 10% on the other five cores.
    I thought more cores were for multi-tasking, as in having multiple programs running simultaneously. It would suck to turn on BF3 and everything else running on my PC simply shut down because the CPU is under 100% utilization. How would i be able to play BF3 while streaming/playing some HD content on my TV that's hooked up to my same computer.


    Reply
  • alidan
    acktionhankGreat article and very informative. The FX-8350 really held it's own until it came down to Skyrim.I thought more cores were for multi-tasking, as in having multiple programs running simultaneously. It would suck to turn on BF3 and everything else running on my PC simply shut down because the CPU is under 100% utilization. How would i be able to play BF3 while streaming/playing some HD content on my TV that's hooked up to my same computer.
    single core performance... look up some other benchmarks, where they use itunes to encode things, or when i believe winzip went from single core to multicore, it shows a GREAT difference more cores can do to performance.

    the problem is that few games and few programs really scale, sure, pro applications almost always take advantage of whatever you put in them, but consumer, different story.

    more cores can offer more multitasking, but they also allow the load to be shifted from one core to all 4 cores and get over all more performance when properly coded.
    Reply
  • Someone Somewhere
    Personally I'd like to see the i5-3570K included in here. It's closer in price to the 8350, but should perform more like the 3770K (as the games are unlikely to use more than 4 threads).
    Reply
  • Crashman
    A Bad DayI disagree. What's needed is even stronger push on the developers to use more than four cores, effectively, not some 100% load on one core and 10% on the other five cores.I'm calling BS on this one because AMD's "eight cores" are actually four modules, on four front ends, with four FP units. Games have historically been limited by FP units specifically and front ends in general, no? What I'm seeing is that Intel's per-core IPC appears to be a little higher, when two different FOUR "full" CORE processors are compared.
    Reply
  • esrever
    There should be an i5 included just so you can have a middle ground.
    Reply
  • amuffin
    I'm really liking the new logo!
    Reply
  • de5_Roy
    like the article.
    woulda liked to see how a 3570k does against the fx8350 running the same cfx setup. impo, the price/perf woulda tipped further in favor of intel in configs like this.
    lastly, woulda liked some newer games like sleeping dogs, far cry3, max payne 3 in the benches instead of the ol' bf3 single player. i hear bf3 sp doesn't stress cpus that much. may be bf3 skewed the benches in favor of amd as much as skyrim favored intel. :whistle:
    Reply
  • quark004
    all these benchmarks are manipulated. First, there is this site which claims the 7900 series does well even with mid level cpus in gaming scenarios. And now toms claim a high end cpu. There is some propoganda here.
    Reply
  • abbadon_34
    It would be nice to see prices for components similar the SMB. Not because I can't look them up, but because the article is very price/performance oriented
    Reply