DirectCompute, OpenCL, and the Future of CAL

As a journalist, GPGPU stuff is one of the more frustrating things to cover. The concept is great, but the execution makes it difficult to accurately cover, exacerbated by the fact that until now AMD and NVIDIA each had separate APIs. OpenCL and DirectCompute will unify things, but software will be slow to arrive.

As it stands, neither AMD nor NVIDIA have a complete OpenCL implementation that's shipping to end-users for Windows or Linux. NVIDIA has OpenCL working on the 8-series and later on Mac OS X Snow Leopard, and AMD has it working under the same OS for the 4800 series, but for obvious reasons we can’t test a 5870 in a Mac. As such it won’t be until later this year that we see either side get OpenCL up and running under Windows. Both NVIDIA and AMD have development versions that they're letting developers play with, and both have submitted implementations to Khronos, so hopefully we’ll have something soon.

It’s also worth noting that OpenCL is based around DirectX 10 hardware, so even after someone finally ships an implementation we’re likely to see a new version in short order. AMD is already talking about OpenCL 1.1, which would add support for the hardware features that they have from DirectX 11, such as append/consume buffers and atomic operations.

DirectCompute is in comparatively better shape. NVIDIA already supports it on their DX10 hardware, and the beta drivers we’re using for the 5870 support it on the 5000 series. The missing link at this point is AMD’s DX10 hardware; even the beta drivers we’re using don’t support it on the 2000, 3000, or 4000 series. From what we hear the final Catalyst 9.10 drivers will deliver this feature.

Going forward, one specific issue for DirectCompute development will be that there are three levels of DirectCompute, derived from DX10 (4.0), DX10.1 (4.1), and DX11 (5.0) hardware. The higher the version the more advanced the features, with DirectCompute 5.0 in particular being a big jump as it’s the first hardware generation designed with DirectCompute in mind. Among other notable differences, it’s the first version to offer double precision floating point support and atomic operations.

AMD is convinced that developers should and will target DirectCompute 5.0 due to its feature set, but we’re not sold on the idea. To say that there’s a “lot” of DX10 hardware out there is a gross understatement, and all of that hardware is capable of supporting at a minimum DirectCompute 4.0. Certainly DirectCompute 5.0 is the better API to use, but the first developers testing the waters may end up starting with DirectCompute 4.0. Releasing something written in DirectCompute 5.0 right now won’t do developers much good at the moment due to the low quantity of hardware out there that can support it.

With that in mind, there’s not much of a software situation to speak about when it comes to DirectCompute right now. Cyberlink demoed a version of PowerDirector using DirectCompute for rendering effects, but it’s the same story as most DX11 games: later this year. For AMD there isn’t as much of an incentive to push non-game software as fast or as hard as DX11 games, so we’re expecting any non-game software utilizing DirectCompute to be slow to materialize.

Given that DirectCompute is the only common GPGPU API that is currently working on both vendors’ cards, we wanted to try to use it as the basis of a proper GPGPU comparison. We did get something that would accomplish the task, unfortunately it was an NVIDIA tech demo. We have decided to run it anyhow as it’s quite literally the only thing we have right now that uses DirectCompute, but please take an appropriately sized quantity of salt – it’s not really a fair test.

NVIDIA’s ocean demo is a fairly simple proof of concept program that uses DirectCompute to run Fast Fourier transforms directly on the GPU for better performance. The FFTs in turn are used to generate the wave data, forming the wave action seen on screen as part of the ocean. This is a DirectCompute 4.0 program, as it’s intended to run on NVIDIA’s DX10 hardware.

The 5870 has no problem running the program, and in spite of whatever home field advantage that may exist for NVIDIA it easily outperforms the GTX 285. Things get a little more crazy once we start using SLI/Crossfire; the 5870 picks up speed, but the GTX 295 ends up being slower than the GTX 285. As it’s only a tech demo this shouldn’t be dwelt on too much beyond the fact that it’s proof that DirectCompute is indeed working on the 5800 series.

Wrapping things up, one of the last GPGPU projects AMD presented at their press event was a GPU implementation of Bullet Physics, an open source physics simulation library. Although they’ll never admit it, AMD is probably getting tired of being beaten over the head by NVIDIA and PhysX; Bullet Physics is AMD’s proof that they can do physics too. However we don’t expect it to go anywhere given its very low penetration in existing games and the amount of trouble NVIDIA has had in getting developers to use anything besides Havok. Our expectations for GPGPU physics remains the same: the unification will come from a middleware vendor selling a commercial physics package. If it’s not Havok, then it will be someone else.

Finally, while AMD is hitting the ground running for OpenCL and DirectCompute, their older APIs are being left behind as AMD has chosen to focus all future efforts on OpenCL and DirectCompute. Brook+, AMD’s high level language, has been put out to pasture as a Sourceforge project. Compute Abstract Layer (CAL) lives on since it’s what AMD’s OpenCL support is built upon, however it’s not going to see any further public development with the interface frozen at the current 1.4 standard. AMD is discouraging any CAL development in favor of OpenCL, although it’s likely the High Performance Computing (HPC) crowd will continue to use it in conjunction with AMD’s FireStream cards to squeeze every bit of performance out of AMD’s hardware.

The First DirectX 11 Games Eyefinity
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  • Wreckage - Wednesday, September 23, 2009 - link

    Hot, loud, huge power draw and it barely beats a 285.

    A disappointment for sure.
  • SiliconDoc - Thursday, September 24, 2009 - link

    Thank you Wreckage, now, I was going to say draw up your shields, but it's too late, the attackers have already had at it.
    --
    Thanks for saying what everyone was thinking. You are now "a hated fanboy", "a paid shill" for the "corporate greedy monster rip off machine", according to the real fanboy club, the ones who can't tell the truth, no matter what, and prefer their fantasiacal spins and lies.
  • Zstream - Wednesday, September 23, 2009 - link

    They still allow you to post?
  • yacoub - Wednesday, September 23, 2009 - link

    He's right in the first sentence but went all fanboy in the second.
  • Griswold - Wednesday, September 23, 2009 - link

    Not really, he's a throughbred fanboy with everything he said. Even on the "loud" claim compared to what previous reference designs vom ATI were like...
  • SiliconDoc - Wednesday, September 30, 2009 - link

    So if YOU compare one loud design of ati's fan to another fan and as loud ati card
    ( they're all quieter than 5870* but we'll make believe for you for now),
    and they're both loud, anyone complaining about one of them being loud is "an nvidia fanboy" because he isn't aware of the other loud as heck ati cards, which of course, make another loud one "just great" and "not loud". LOL

    It's just amazing, and if it was NV:

    " This bleepity bleep fan and card are like a leaf blower again, just like the last brute force monster core power hog but this **tard is a hurricane with no eye."

    But since it's the red cards that are loud, as YOU pointed out in the plural, not singular like the commenter, according to you HE's the FANBOY, because he doesn't like it. lol

    ULTIMATE CONCLUSION: The commenter just told the truth, he was hoping for more, but was disappointed. YOU, the raging red, jumped his case, and pointed out the ati cards are loud "vom" prior.. and so he has no right to be a big green whining fanboy...
    ROFLMAO
    I bet he's a "racist against reds" every time he validly criticizes their cards, too.
    ---
    the 5870 is THE LOUDEST ATI CARD ON THE CHART,AND THE LOUDEST SINGLE CORE CARD.
    --
    Next, the clucking rooster will whiplash around and flap the stubby wings at me, claiming at idle it only draws 27 watts and is therefore quiet.
    As usual, the sane would them mention it will be nice not playing any 3d games with a 3d gaming card, and enjoying the whispery hush.
    --
    In any case:
    Congratulations, you've just won the simpleton's red rooster raving rager thread contest medal and sarcastic unity award.(It's as real as any points you've made)

    Anyhow thanks, you made me notice THE 5870 IS THE LOUDEST CARD ON THE CHARTS. I was too busy pointing out the dozen plus other major fibboes to notice.
    It's the loudest ati card, ever.
  • GourdFreeMan - Wednesday, September 23, 2009 - link

    I thought the technical portion of your review was well written. It is clear, concise and written to the level of understanding of your target audience. However, I am less than impressed with your choice of benchmarks. Why is everything run at 4xAA, 16xAF? Speaking for most PC gamers, I would have maxed the settings in Crysis Warhead before adding AA and AF. Also, why so many console ports? Neither I, nor anyone else I personally know have much interest in console ports (excluding RPGs from Bethesda). Where is Stalker: Clear Sky? As you note its sequel will be out soon. Given the short amount of time they had to work with DX11, I imagine it will run similarly to Stalker: Call of Pripyat. Also, where is ArmA II? Other than Crysis and Stalker it is the game most likely to be constrained by the GPU.

    I don't want to sound conspiratorial, but your choice of games and AA/AF settings closely mirror AMD's leaked marketing material. It is good that you put their claims to the test, as I trust Anandtech as an unbiased review site, but I don't think the games you covered properly cover the interests of PC gamers.
  • Ryan Smith - Wednesday, September 23, 2009 - link

    For the settings we use, we generally try to use the highest settings possible. That's why everything except Crysis is at max quality and 4xAA 16xAF (bear in mind that AF is practically free these days). Crysis is the exception because of its terrible performance; Enthusiast level shaders aren't too expensive and improve the quality more than anything else, without driving performance right off a cliff. As far as playing the game goes, we would rather have AA than the rest of the Enthusiast features.

    As for our choice of games, I will note that due to IDF and chasing down these crazy AA bugs, we didn't get to run everything we wanted to. GRID and Wolfenstein (our OpenGL title) didn't make the cut. As for Stalker, we've had issues in the past getting repeatable results, so it's not a very reliable benchmark. It also takes quite a bit of time to run, and I would have had to drop (at least) 2 games to run it.

    Overall our game selection is based upon several factors. We want to use good games, we want to use popular games so that the results are relevant for the most people, we want to use games that give reliable results, and ideally we want to use games that we can benchmark in a reasonable period of time (which means usually having playback/benchmark tools). We can't cover every last game, so we try to get what we can using the criteria above.
  • GourdFreeMan - Thursday, September 24, 2009 - link

    Popularity and quality are strong arguments for World of Warcraft, Left 4 Dead, Crysis, Far Cry, the newly released Batman game... and *maybe* Resident Evil (though it is has far greater popularity among console gamers). However, HAWX? Battleforge? I would never have even heard of these games had I not looked them up on Wikipedia. In retrospect I can see you using Battleforge due to it being the only DirectX 11 title, but I still don't find your list of games compelling or comprehensive.

    To me *PC* gaming needs to offer something more than simple action to justify its cost of entry. In the past this included open worlds, multiplayer, greater graphical realism and attempts at balancing realistic simulation with entertaining game play. Console gaming has since offered the first two, but the latter are still lacking.

    It's games like Crysis, Stalker and ArmA II along with the potential of modding that attract people to PC gaming in the first place...
  • dvijaydev46 - Wednesday, September 23, 2009 - link

    Good review but it would be good if you could also add Steam and Cuda benchmarks. Now you have a common software Mediashow Espresso right?

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