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Heterogeneous Computing

CPU and GPU tests would have been sufficient for benchmarking hybrid processors in the past, but now there’s a lot of applications that can make use of both types of computing cores simultaneously. Such heterogeneous applications utilize the OpenCL 1.1 framework which provides methods for executing computations on the graphics core’s shader pipelines. AMD claims that the majority of multimedia content authoring and processing applications can effectively use all the computing resources offered by today’s APUs. The prospective HSA concept is supposed to make the combined use of CPU and GPU resources easier.

HSA is still far from practical implementation, but there are already applications which can use the GPU via OpenCL 1.1. These include free software…

…as well as commercial products.

Ideally, we wouldn’t want to use special tests to check out OpenCL performance. It would be better if hybrid processors were natively supported by everyday applications including those we use for our standard performance testing. But today heterogeneous computing is not implemented widely. In most cases OpenCL acceleration is only used for specific operations and we need specific tests to see it. That's why we have to dedicate a special section of our review to heterogeneous computing.

Talking about the performance benefits ensured by hybrid processors, AMD uses synthetic benchmarks. Of course, it is easier to develop a special algorithm that can showcase the benefits of heterogeneous computing rather than to redesign an existing application.

So the most popular OpenCL benchmark is Basemark CL. It helps test an APU at three types of tasks: image processing (noise reduction, antialiasing and sharpening), physics modeling (hydrodynamic and wave processes, soft substance modeling), and fractal generation.

It goes without saying that specific tasks can enjoy a huge performance boost via GPU resources. Basemark CL is meant to showcase the computing potential of today's integrated graphics cores. AMD’s APUs have more advanced graphics cores, so their computing potential is higher. With OpenCL optimizations enabled, the A10-7850K is almost twice as fast the Intel’s processors. AMD puts an emphasis of such test results, suggesting that AMD APUs may be superior to their opponents in a world where most resource-consuming applications use both x86 and graphics resources. The question is whether we will ever live in such a world, too.

Now let’s see what we have in actual applications rather than synthetic benchmarks. As usual, we will start out with WinZIP which has been supporting OpenCL since its last version. Like in many other real-life applications, the GPU-based acceleration doesn't work always in WinZIP. The utility only applies it to compressing files larger than 8 megabytes. We don't want to handpick any files, so we just compress a folder with an Adobe Photoshop CC distribution.

WinZIP’s OpenCL acceleration doesn’t produce a big effect and cannot change the overall picture. Intel processors used to be faster in compression tests, so they remain in the lead with OpenCL, too. Moreover, the Haswell processors enjoy a larger performance boost from OpenCL than the Kaveri or Richland do.

The latest versions of the Libre Office suite have introduced experimental OpenCL support. Particularly, the Calc application may apply GPU resources to computing formulas. In our test we measure the time it takes to recalculate a spreadsheet with financial data.

The OpenCL optimization is not yet polished off in Libre Office Calc, so we can even see a performance hit when the GPU is used for computing. The Kaveri APUs can’t beat Intel’s Haswell processors irrespective of whether the OpenCL support is turned on or off.

The popular image editing application Adobe Photoshop CC is also declared to support OpenCL. However, this support is limited to only a few filters. AMD recommends benchmarking performance while applying the Smart Sharpen filter. We do so with a 24-megapixel image in our test.

Everything works exactly as it should in this case. The Smart Sharpen filter works faster with GPU-based acceleration on both AMD and Intel processors. The Kaveri-based configuration enjoys a larger performance boost than the other systems, yet the A10-7850K is still inferior to both the Core i5-4430 and the Core i3-4340 even with the OpenCL optimization turned on. It is just important to have fast x86 cores for Photoshop.

Another example of a popular OpenCL-compatible application is the professional video editing tool Sony Vegas Pro 12. When rendering video, it can distribute the load among all the computing resources of hybrid processors.

Just like in the previous test, AMD’s APUs enjoy a substantial performance boost after we enable OpenCL acceleration in Sony Vegas. It amounts to 60% but can't help them beat their Intel opponents. The fact is Intel's Haswell processors support OpenCL, too, and thus accelerate in the same manner. Besides, even with the GPU resources in use, the performance of the x86 cores remains most important. So AMD’s claims that the fast integrated graphics core and software optimizations will make AMD APUs superior to Intel’s hybrid processors do not seem to come true.

HD video transcoding is a special topic when it comes to heterogeneous computing. Intel processors feature a special Quick Sync engine for that purpose which provides hardware transcoding acceleration. AMD offers its VCE engine with the same functionality but it is not used in practice. Instead, the existing applications make use of OpenCL to accelerate video transcoding. To check out the performance benefits, we will run MediaCoder 0.8.28. We transcode an original 1080p@50fps AVC file from the x264 FHD Benchmark 1.0.1 with a bitrate of about 30 Mbps.

The OpenCL acceleration for video transcoding helps ensure certain performance benefits for AMD processors but can't make them competitive to Intel's products with Quick Sync. The high efficiency of the hardware Quick Sync acceleration can’t be achieved with any other means as yet.

Summing it up, we can say that the new Kaveri APUs cannot offer the same performance as comparably priced Intel Haswell processors even in heterogeneous computing applications available today. Theoretically, this may change with the implementation of HSA, but we can’t really be sure about the benefits of HSA and whether it will be implemented at all.

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