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A More Capable GPU: GCN Surfaces In Kaveri

AMD A10-7850K And A8-7600: Kaveri Gives Us A Taste Of HSA
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I’m a bit of geek in that I get excited about testing the differences between subsequent processor designs. But Steamroller really only serves as an enabler for AMD’s Graphics Core Next architecture in Kaveri, improving IPC enough so that the more dense APU doesn’t sacrifice too much general-purpose performance as the graphics subsystem grows. In fact, AMD says Kaveri’s GPU accounts for 47% of the die.

The engine is composed of up to eight GPU “cores”, formerly referred to as Compute Units, and made up of four Vector Units with 16 shaders each. In total, that’s 64 shaders per core and 512 shaders in an eight-core implementation. Don’t let the numbers or evolving terminology confuse you though. Architecturally, this is the same technology found in AMD’s Hawaii GPU, which I covered in Radeon R9 290X Review: AMD's Back In Ultra-High-End Gaming, including precision improvements to the native LOG/EXP operations and MQSAD optimizations for speeding up motion estimation algorithms, mentioned back when Hawaii launched. Of course, the big addition is coherent shared unified memory. That coherency makes it easier to pass data between the GPU and CPU cores—again, the degree of “equalness” between dissimilar on-die resources is the exact reason why AMD is using the term Compute Core to begin with.

There’s a lot of strategic trimming that goes into optimizing Kaveri’s GPU compared to AMD’s discrete solutions. The Hawaii GPU has four geometry processors able to rasterize as many primitives per clock cycle. Tahiti features two. Kaveri gets one. And while 16 render back-ends give Hawaii massive pixel fillrate, Kaveri is pared down to two ROP partitions, capable of eight pixels per clock. Given the bandwidth limitations of an integrated solution attached to DDR3 memory, those design decisions make perfect sense.

Not every piece of the Kaveri GPU is a subset of Hawaii. AMD exposes all eight of the discrete processor’s Asynchronous Compute Engines, which independently schedule tasks to the CUs (incidentally, Sony’s PlayStation 4 also boasts eight ACEs). They all share access to a global data share and a 512 KB L2 cache. But they can otherwise operate on their own for efficient multi-tasking. Back when I was digging into Hawaii, the shift from two ACEs in Tahiti to four in Kabini/Temash and then eight didn’t seem imminently necessary. Now that we’re seeing the design exposed on Kaveri, however, its importance to AMD’s HSA is clearer. 

Fixed-Function Accelerators: More Specialized Hardware

I already mentioned that Kaveri lacks fixed-function support for H.265 decoding. However, the old faithful Unified Video Decoder is in there, accelerating playback of H.264, VC-1, MPEG-2, MVC, and MPEG-4. In essence, the “new” UVD 4 in Kaveri is similar to the older UVD 3 block, except for improved error resiliency during AVC decoding.

AMD also claims to have improved its Video Codec Engine, adding I, P, and B frame support to the common H.264 YUV420 video format and I frames to the simpler YUV444 format. To be sure, we’re happy to see AMD adding to the VCE block’s functionality. However, our most recent look at the VCE’s performance put AMD behind Nvidia’s NVEnc solution and significantly slower than Intel’s Quick Sync. So, while Kaveri’s second-gen VCE might represent a functional step forward, we want to see more attention paid to its position relative to competitive encoders.


As with the Hawaii and Bonaire GPUs powering Radeon R9 290X, 290, and R7 260X, Kaveri includes TrueAudio support. That means there are, presumably, three Tensilica HiFi2 EP Audio DSP cores built into the APU’s die able to offload sound processing. I say Kaveri supports this technology because it needs to be exploited in software before you realize any benefit, and thus far there aren’t any applications we can use to illustrate TrueAudio’s impact. At least in practice, it’s intended to facilitate more complex effects without a corresponding drain on host resources. But every attempt we’ve seen to demonstrate TrueAudio hasn’t translated particularly well to a conference room setting.

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  • 13 Hide
    vertexx , January 16, 2014 5:30 AM
    While the gaming enthusiast may not have much here to get excited about, I think the real story here is the A8-7600. Especially at 45W, the numbers are quite impressive for this part.

    Of course, the other part of this story will be the adoption of HSA and Mantle. In this regard, I think AMD is playing its cards right. If you want to provide incentive for game developers to invest in developing for Mantle, that economic incentive is not going to come from providing a high-end part that tries to compete with high-end discrete GPUs. That economic incentive, and I believe it's huge, is in lowering the cost of entry to play your game.

    With the A8-7600, I believe AMD is providing a tremendous market opportunity and incentive if, with the combination of Kaveri plus embedded technologies (Mantle & True Audio), you can provide a playable gaming environment for the mass market. Admittedly, it may not be a "playable gaming environment" from an enthusiast standpoint, but as an entry point, it is quite good enough. It will be important for AMD to show that the release of Mantle for BF4 impacts performance for the Kaveri APUs in particular. More specifically, they will need to show that Mantle makes BF4 playable on a 7600. If they are successful in that regard, then I think they may really have something exciting here.

    I'm hoping AMD is successful in this, because it's obvious that the desktop CPU performance race has reached a point of diminishing returns. Kudus for AMD for potentially changing the game in the industry.

    All that said, they screwed up the pricing for the high-end. It needs to be $30 cheaper, and what is even the point of the 7700K? The 7850K at ~$145 and the 7600 where it is would have made much more sense if they want to incent adoption of this technology. The other point is they need to get motherboard manufacturers on-board with bringing more ITX FM2+ motherboards to market at different price points.
  • 11 Hide
    Someone Somewhere , January 16, 2014 4:23 AM
    Quote:
    A10-7850k is slower than A10-6800K ?? WTF.


    I got the opposite impression. Which graph are you looking at?
Other Comments
  • 0 Hide
    vipervoid1 , January 16, 2014 3:54 AM
    Somethings with Diagram u provided at page 9 ~ Core i5 4760k @@Please fix that ~
  • 1 Hide
    Someone Somewhere , January 16, 2014 4:10 AM
    Yeah, almost all the diagrams refer to the 4760K.

    Given that AM3+ looks like it's done, it would have been nice to see a 6-core chip. Still, one of these may end up in my next laptop.
  • 1 Hide
    cangelini , January 16, 2014 4:21 AM
    Will get the charts fixed shortly--thanks for the catch!
  • 11 Hide
    Someone Somewhere , January 16, 2014 4:23 AM
    Quote:
    A10-7850k is slower than A10-6800K ?? WTF.


    I got the opposite impression. Which graph are you looking at?
  • 8 Hide
    Jaroslav Jandek , January 16, 2014 4:24 AM
    Thank you for the article (especially the power consumption measurements), Chris. It is definitely an improvement over Richland but kind of boring (disappointingly expectable).

    I really like where AMD is going (HSA, GCN and TrueAudio).Too bad the manufacturing process of GlobalFoundries just can't match Intel's.

    Also, it would be interesting to see the new Bay Trail Pentium or Celeron CPUs (whichever is closer in performance) in the Efficiency graphs.
  • -1 Hide
    Someone Somewhere , January 16, 2014 4:25 AM
    I'm fairly sure that this is on TSMC's 28nm node. GlobalFoundries can't do that yet; this is on the same process used for AMD GPUs currently.
  • 0 Hide
    Jaroslav Jandek , January 16, 2014 4:45 AM
    Quote:
    I'm fairly sure that this is on TSMC's 28nm node. GlobalFoundries can't do that yet; this is on the same process used for AMD GPUs currently.

    28nm SHP from GlobalFoundries. AMD bought over $1 billion worth of wafers from them in december...

    I guess you have been reading the articles from a year ago about AMD still using TSMC despite promises of GlobalFoundries' new 28nm SHP process.
  • 9 Hide
    jacobian , January 16, 2014 5:12 AM
    I don't really believe into the whole HSA smoke-screen. By the time HSA-enabled apps take off, you will be ready to upgrade from your CPU again. The one terrible truth that stands out right now is that at current prices, the flagship Kaveri A10 doesn't make any sense whatsoever. Kaveri A8? Maybe. Richland A10-6790K? Perhaps. But the Kaveri A10 at $180 is a just a joke, specially after all that hype.
  • 3 Hide
    Someone Somewhere , January 16, 2014 5:16 AM
    CPUs are usually released at ridiculous prices, and come down over a month or two.
  • 13 Hide
    vertexx , January 16, 2014 5:30 AM
    While the gaming enthusiast may not have much here to get excited about, I think the real story here is the A8-7600. Especially at 45W, the numbers are quite impressive for this part.

    Of course, the other part of this story will be the adoption of HSA and Mantle. In this regard, I think AMD is playing its cards right. If you want to provide incentive for game developers to invest in developing for Mantle, that economic incentive is not going to come from providing a high-end part that tries to compete with high-end discrete GPUs. That economic incentive, and I believe it's huge, is in lowering the cost of entry to play your game.

    With the A8-7600, I believe AMD is providing a tremendous market opportunity and incentive if, with the combination of Kaveri plus embedded technologies (Mantle & True Audio), you can provide a playable gaming environment for the mass market. Admittedly, it may not be a "playable gaming environment" from an enthusiast standpoint, but as an entry point, it is quite good enough. It will be important for AMD to show that the release of Mantle for BF4 impacts performance for the Kaveri APUs in particular. More specifically, they will need to show that Mantle makes BF4 playable on a 7600. If they are successful in that regard, then I think they may really have something exciting here.

    I'm hoping AMD is successful in this, because it's obvious that the desktop CPU performance race has reached a point of diminishing returns. Kudus for AMD for potentially changing the game in the industry.

    All that said, they screwed up the pricing for the high-end. It needs to be $30 cheaper, and what is even the point of the 7700K? The 7850K at ~$145 and the 7600 where it is would have made much more sense if they want to incent adoption of this technology. The other point is they need to get motherboard manufacturers on-board with bringing more ITX FM2+ motherboards to market at different price points.
  • 1 Hide
    Au_equus , January 16, 2014 5:40 AM
    There appears to a typo or at least a contradiction on the table (first page), which lists the A10-7700K with 512 shaders. The paragraph below then says it has 384 shaders.
  • 3 Hide
    Nossy , January 16, 2014 5:40 AM
    Basically at this point it is not worth the premium $50-60USD or so over Richland and Trinity. At $180, you can get an i5 3570k at some places like Microcenter. Another disappointing release from AMD.
  • 0 Hide
    The_Trutherizer , January 16, 2014 5:51 AM
    I'm extremely excited to see the results from more HSA compliant apps myself. Some of the benchmarks I have seen are beastly.I'm really starting to think that the APU is a superior approach. With x86 performance past a certain point CPUs with traditional cores will be relegated to specialised servers in the eyes of consumers. I mean how quickly do you want to open an excel spreadsheet or encode or decode music and video? 0.5s or 0.3s?
  • 8 Hide
    nezzymighty , January 16, 2014 5:52 AM
    Quote:
    With the A8-7600, I believe AMD is providing a tremendous market opportunity and incentive if, with the combination of Kaveri plus embedded technologies (Mantle & True Audio), you can provide a playable gaming environment for the mass market. .... they may really have something exciting here.
    @ vertexx ... finally a non troll or die hard Intel/AMD fan that is making sensible points...I used to be a gamer and spent thousands, being a die hard fan of one today's chip makers. Now, as a mainstream user that has to use their money towards real life applications (rather than FPS) like a house, family, children, eating, paying bills, etc... I tend now to look for a solution to spend the disposable income on a solution that is cheap but encompasses the ability to do a little of everything...Well done AMD... please keep the innovation coming, and competition alive too keep prices down for all to enjoy...
  • 1 Hide
    rolli59 , January 16, 2014 5:54 AM
    Well if this is the future from AMD they are going to leave Intel alone in the high end gaming space.
  • -2 Hide
    styrkes , January 16, 2014 5:55 AM
    This measly increase in performance is just shoddy. Wonder what amazing story and hype AMD will put out for their next APU. I'm pretty much done with all this new advanced technology that's supposed to bring increased efficiency, performance, etc. etc. They've been doing this ever since they released their first APU. The next time AMD releases their next APU, I'll just jump straight into the benchmarks, see if that's any good.
  • -8 Hide
    styrkes , January 16, 2014 5:56 AM
    This measly increase in performance is just shoddy. Wonder what amazing story and hype AMD will put out for their next APU. I'm pretty much done with all this new advanced technology that's supposed to bring increased efficiency, performance, etc. etc. They've been doing this ever since they released their first APU. The next time AMD releases their next APU, I'll just jump straight into the benchmarks, see if that's any good.
  • 2 Hide
    Trachu , January 16, 2014 6:02 AM
    A8-7600 paired with R9-240 looks like a good deal. I belive this is a great Chance for AMD here if it sorts Crossfire performance things right Here lays the whole reason to buy APU instead of plain CPU.Why you have not commented about it in your final words when you thought about the alternatives?
  • 6 Hide
    logainofhades , January 16, 2014 6:32 AM
    Quote:
    Basically at this point it is not worth the premium $50-60USD or so over Richland and Trinity. At $180, you can get an i5 3570k at some places like Microcenter. Another disappointing release from AMD.


    Yesterday there was an HD7770 so low that you could get that and an FX 6300 for like $5 more than what newegg is asking for the 7850k. You can get an HD 7750 in that general price range with an FX 6300 now. In desktop, APU's still hold no appeal to me at all. Mobile, they have promise for sure.
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