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Crossfire Revelation.

Discussion in 'Desktops' started by Fallout3, Apr 12, 2013.

  1. Fallout3

    Fallout3 Member

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    Hi all. I've been meaning to do a write up on this latest information and I've finally found some time to do it today. In short though there is a huge issue with Crossfire that has only just been discovered.

    Right, so Crossfire. It's supposedly faster than SLI and scaling is better. But is it? the short answer is no, it's terribly broken and under no instances should you consider running it.

    Why? well this is where it gets a bit more complicated. A technology has been doing the rounds lately called FCAT. It is an open source software app that reads the types of frames being put out by your graphics card/s and applies coloured bands to the side of the picture.

    So how does it work?

    FCAT reads frames per second in a similar way to FRAPS. However, FRAPS is recorded at a low level and does not differentiate the types of FPS you are being sent.

    The main issue with these latest findings is Runt frames and, Dropped frames. I will explain what these are in just a second..

    OK, so what is a Runt Frame ? a runt frame is a frame that is 5 pixels high in size. It is the true, factual name for a Micro stutter. When decoded and looked at in the instance it displays it does this.

    [​IMG]

    IE displays the runt frame right in the middle of a proper frame. Runt frames cause stutter and tearing.

    Dropped Frames. These are frames per second that are briefly displayed at a low level, yet, are not carried out so don't count.

    So now that we have covered the problems being faced here let's put them into context a little. Runt frames damage your gaming experience by causing stutter and tearing, dropped frames don't count. So how do you go about seeing them and recording them?

    That is explained at a technical level here.

    Frame Rating Dissected: Full Details on Capture-based Graphics Performance Testing - PC Perspective - YouTube

    So how does this technology work? Basically FCAT is used to display coloured bars on the side of the game in question. From there a high speed capture device is used in a separate PC and the signal output from the GPU set up PC is sent to the capture device. This technology records a 30 second clip at around 25gb so the hardware being used to capture needs to keep up. In order to do this a huge RAID array of SSDs is used..

    So what happens once the video has been recorded onto the capture machine? well, FCAT then reads the video that has been recorded and from there it outputs the data to a XML file. Once done the XML file removes runt and dropped frames and we end up with Observed FPS IE - the actual frames per second you see on your monitor, not the low level reading that FRAPS outputs.

    You can find examples of this here.

    Frame Rating: GTX 660 vs HD 7870, plus HD 7790, HD 7850, GTX 650 Ti BOOST | PC Perspective

    For the lower end models in Crossfire and SLI and here.

    Frame Rating Dissected: Full Details on Capture-based Graphics Performance Testing | PC Perspective

    Which covers Titan, the 690, 7990 and so on.

    So what does this all mean?

    Well basically it exposes Crossfire for being terribly problematic. There isn't really any way of buttering it up, Crossfire fails to work in over 50% of the games on the market right now and is sending out completely false FPS readings. SLI on the other hand? displays no such issues. People who thought their Crossfire set ups were working correctly and outputting very high FPS scores that competed with, and in most cases beat, SLI were basically fooled by AMD.

    AMD are completely aware of this issue of course, and have made a comment to say that they would look into it. Of course they knew it was happening all along (they must have done) yet decided not to be outgoing with this information.

    So what if you are running a 7970 or lower? do they come with the same issue? No. The answer is no, this does not apply to single Radeon cards, only Crossfire X.

    What about SLI? of course SLI does come with its own issues but certainly not with runt or dropped frames. It's fair to say that with SLI what you see is pretty much what you get.

    This issue is also not relevant to any single Nvidia card either, it only applies to Crossfire X.

    So what's the upshot?

    Basically for now it would be absolutely crazy to even consider a Crossfire X set up. At least not until AMD have gone back to the drawing board and manage to resolve these issues. It's just a clear cut case of not getting what you see. Ryan (the guy using this technology) is also going to look at cards from the past to see just how long this has been going on for so please keep an eye on PC Perspective | Your #1 Source for PC Hardware Reviews, News and Information! for updates and future testing.


    Now before I am accused of being biased or a fanboy? yes I run SLI. I've also used many SLI systems in the past. However,I've also used a lot of Crossfire X systems and each one has driven me crazy with the stuttering and driver issues. I'm not saying SLI does not come with its issues because it does. It took over a month for Nvidia to fix Far Cry 3 in SLI. However,once a game generally works in SLI it works properly..

    Thanks for reading and I hope this information proves useful and saves you from wasting money on a second GPU that will actually damage your gaming experience.

    Andy (FO3)
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  2. hlpmeimdrowning

    hlpmeimdrowning Member

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    Very interesting. Cheers!
  3. Fallout3

    Fallout3 Member

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    No problems :)

    I will update with more information as and when. Other sites have been using this technology for a while to dissect frame times and latency but as of now only PCper and overclockersclub have used it to remove runt and dropped frames.
  4. rjw3715

    rjw3715 Member

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    I remember hearing about this recently.

    I think it may have been on one of Linus' live streams but not entirely sure.

    Definitely put me off Crossfire as it stands.
  5. Fallout3

    Fallout3 Member

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    It's slowly being adopted widespread now as a means to record actual on screen FPS.

    FRAPS reads the frames here.

    [​IMG]

    Where as this card...

    [​IMG]

    Can record a video of what's being spat out of the end.

    As an example to what happens when the 'pointless' frames are removed take a look at this.

    This is Battlefield 3 on 7970 CFX at GPU level.

    [​IMG]

    And here is what is actually happening on the monitor when the runt frames and dropped frames are removed.

    [​IMG]

    Just to point out this isn't some sort of AMD hate spiel, it's just the truth. Sadly it actually gets worse when used on pairs of lower models. The problem just becomes even more apparent to the point that only about 40% of the games tested actually work properly.
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  6. malky78

    malky78 Member

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    Thanks for the write up Fallout3. I had no clue about this. I've only ever run SLI. It's a pity reviewers (big ones) don't make mention of this.

    It's purely by chance / good fortune that I'm running SLI this time around rather than CFX. Over the years I've alternated between ATI / Nvidia. I've personally stuck with Nvidia this / last generation as I played a lot of Borderlands 2.
  7. MrGrumpie

    MrGrumpie Active Member

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    Is this true?

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