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


View All Comments

  • Qfromchicago - Friday, November 27, 2009 - link

    Windows 7 Profession
    Onkyo 805
    Diamond 5870
    Still no 3rd option for hd audio.

    Has anyone been able to work this thing
  • charme - Friday, November 27, 2009 - link

    same here.
    no 3rd option for hd audio
  • otni - Sunday, November 29, 2009 - link

  • FlyTexas - Saturday, November 14, 2009 - link

    What good does it do to launch this, if there are still none for sale a month later?

    Yes, I know there were a few sold up front, but NewEgg has been out for awhile...
  • RavnosCC - Tuesday, November 17, 2009 - link

    The 57xx series are readily available, they also support HD Audio. Reply
  • RavnosCC - Monday, November 23, 2009 - link

    "As of today, new PowerDVD 9 Ultra customers will receive build 2320, which includes support for HDMI bitstreaming of undecoded (full quality) audio with ATI Radeon 5000 series graphics cards, and the Auzentech X-Fi Hometheater HD sound card. An update patch for current owners of PowerDVD 9 Ultra is scheduled to be available next Friday (11/27).

  • Qfromchicago - Wednesday, November 25, 2009 - link

    Though happy that finally we will get hd audio using powerdvd, but why limit it to new customers only. It seems to me that if you can offer it to new customers, you should be able to offer it to everyone at the same time. Reply
  • Qfromchicago - Sunday, October 18, 2009 - link

    I have win 7, a diamond 5870, powerdvd 9 ultra version 2201 and still I don't get he 3rd choice for the HD audio bitstreaming. Has anyone been able to get bitstreaming to work with powerdvd 9. Thanks Reply
  • RavnosCC - Thursday, November 5, 2009 - link

    UPDATE: Looks like late November for the mythical patch...

    "Hi everyone,
    Yes... we read these forums regularly. Feedback is forwarded to the appropriate people. These forums aren't the best way for us to provide customer support, so if you have an issue, please open a support ticket through our website.

    We can't always comment on new developments... or at least we like to wait until we have a definite answer. I know everyone noticed the reviews for the ATI Radeon 5000 series graphics cards, where certain reviewers were using a pre-release version of PowerDVD 9 to demonstrate HDMI bitstreaming of Blu-ray audio. Support for this feature will be in the next PowerDVD update (patch), which will be available later this month. I don't have a firm date on this, but we're trying to expedite it. Please keep in mind that each of our regular updates includes fixes for new BD titles and new (or forthcoming) hardware / drivers across the PC ecosystem, and so the feature you are anxiously waiting for isn't the only thing that we need to include in the update. Of course, each update has to go through a full quality assurance testing procedure, to make sure that none of the changes introduced any new issues.

    So... sorry for going quiet on you... but I and others read every post in this thread and other relevant threads, following up as needed (in some cases, directly through private messages on these forums).

  • RavnosCC - Wednesday, October 28, 2009 - link

    I am in the same boat, with Vista, I have powerdvd 9 ultra fully patched and still no third option for hi-def passthrough... :-/ Reply

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