AMD's A-Sync DMA Code Makes For Fast Performance
Written by Michael Larabel in AMD on 12 December 2012 at 01:35 PM EST. 21 Comments
After the benchmarks of the Radeon Gallium3D sub-allocator that in some tests yields more than a 25% performance boost, initial testing was done of the new AMD a-sync DMA engine support for the open-source Radeon driver.

Earlier this week AMD released code to support the a-synchronous DMA engines. This support goes from the Radeon HD 2000 series up through the very latest Radeon HD 7000 series graphics hardware. The DRM side of this code will be merged into the Linux 3.8 kernel while other user-space code is still forthcoming.

Christian K├Ânig of AMD described the a-sync DMA code as "The async DMA can do copy/moves independent of the shader engine. So while the shader part of the GPU is busy with the rendering we can still upload new data with the DMA at the same time. Additional to that it is quite a bit more efficient than the shader engine when you just want to copy some data from A to B, or just clear a specific region of memory (memcpy/memset). So using it should result in some very nice performance improvements for certain use cases, but what Alex has released is just kernel part of the implementation, and even that is missing the CS checker. It will probably just take some more time till mesa really picks that up."

Aaron Watry, the Phoronix reader who carried out the simple Radeon Gallium3D sub-allocator tests using the Phoronix Test Suite and OpenBenchmarking.org, has now begun tests on the Radeon DRM code for this a-sync DMA engine support.

Using an AMD Radeon HD 6850 graphics card on the open-source Linux graphics driver stack, Aaron is reporting nearly a 10x improvement in performance for Unigine Heaven as a result of this new code for Linux 3.8.

He notes these early results in this forum post and says he will be conducting additional tests soon. For those wanting to see the initial performance data of this new code from AMD, the data is within the async_dma_tests result file.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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