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[Legit]AMD DirectX 11 White Paper Released
Quote:
DirectX 11 is about efficiency
With Microsoft Windows 7 set to be released in October 2009, rumors are flying rampant in the video card industry as DirectX 11 graphics card will also be launching at the same time. As many of our readers are already aware AMD has already been pushing DirectX 11 as the next be step for graphics. Those who read Legit Reviews will remember AMD started promoting DirectX 11 all the way back to August 2008 when they discussed plans to add full support for DirectX 11 in their Stream Software Development Kit (SDK). More recently on June 2nd, 2009, AMD actually demonstrated tessellation on the worlds first DirectX 11 graphics processor! AMD says they are on track to launching their 'Evergreen' series of DirectX 11 cards around the time Microsoft Windows 7 launches, which makes sense due to all the marketing hype they are trying to build.
Some of the guys up in Toronto sent us an e-mail this morning and explained that DirectX 11 is important and we should take NVIDIA downplaying it with a grain of salt. It seems they are worried that the tried and true NVIDIA marketing machine will possibly start pumping out a lot of information to deflect and sway consumers. This is likly going to be the case as NVIDIA is rumored to be late to the game with DirectX 11 graphics cards and is going to have a rough time to get them released this calendar year. To help avoid this looming marketing battle, AMD has released a whitepaper that has been put together by AMD to showcase the importance of DirectX 11 and why it matters. They also gave us quick breakdown explaining that DX 11 is about efficiency.
* Improved Parallelism
* Improved Precision and Integer Processing
* Tight Integration between Compute Shaders and Rendering Pipeline
* Improved Ease of Programming and Better Memory Usage Efficiency
Many of the DX 11 compute features are very technical and programming oriented, so they released this white paper to make sure the public understands the features and there importance going forward. That being said we will let you read the white paper and make your own conclusions on the importance of DirectX 11. Just looking at the leaked DirectX 11 screen shots, we would think that many would be impressed. 
AMD – DirectX 11 Compute
DirectX11 is the latest industry standard programming interface from Microsoft that provides accessto the advanced capabilities of next generation GPUs. It will be a key component of the new Windows 7 operating system, and Microsoft plans to eventually support it on Windows Vista as well with a software update.
One of the key new features of DirectX 11 is support for DirectX Compute, which enables developers to utilize the massive parallel processing power of modern GPUs to accelerate a much wider range of applications that were previously only executable on CPUs. Accessed via programs called Compute Shaders that are executed on the GPU, they can be used to enable new graphical techniques (such as order independent transparency, ray tracing, and advanced post-processing effects), or to accelerate a wide variety of non-graphics applications (such as video transcoding, video upscaling, game physics simulation, and artificial intelligence).
Today’s GPUs offer orders of magnitude more raw processing power than today’s CPUs for a given cost or power budget. However, as application-specific processors, GPUs lack some of the flexibility of CPUs, which can make it challenging for developers to access their full potential. More recent GPUs include new features designed to improve their flexibility and make these challenges easier to overcome. Another challenge has been coming up with a unified programming model for DirectX Compute that works across a range of different GPU architectures with varying capabilities. The DirectX 11 programming interface handles this by including a set of profiles called Shader Models. Each Shader Model includes a superset of the features in lower versions. Benefits of higher shader models include:
* Improved Parallelism
* Improved Precision and Integer Processing
* Tight Integration between Compute Shaders and Rendering Pipeline
* Improved Ease of Programming and Better Memory Usage Efficiency
One advantage of Compute Shaders over other programming models for parallel processors is that they share a unified instruction set with other shader types used for graphics programming, such as Pixel Shaders and Vertex Shaders. So although Compute Shaders are a new feature of DirectX 11, some Shader Models with reduced features sets can run on earlier hardware, as follows:
* Shader Model 4.0 - DirectX 10 class or newer GPUs
* Shader Model 4.1 - DirectX 10.1 class or newer GPUs
* Shader Model 5.0 - DirectX 11 class GPUs only
This allows developers to choose between maximizing compatibility by choosing a lower Shader Model,or simplifying development and maximizing performance by using a higher Shader Model.
White Paper Continued
Many interesting algorithms and techniques will really only be possible or practical to implement on upcoming DirectX 11-enabled GPUs that support Shader Model 5.0. Here is a summary of some of the key advantages Shader Model 5.0 offers over Shader Model 4.0:
These features are described in more detail below.
1. Improved Parallelism - The following features of DirectX 11-enabled GPUs greatly enhance a programmer’s ability to exploit parallelism:
* Increased Thread Group Size and 3D Thread Dispatch: A Thread Group is a set of threads that work together to efficiently implement a partitioned data parallel algorithm. DirectX 11-enabled GPUs improve the efficiency of memory accesses by allowing the coherent exchange of data between threads within a group, thus enabling parallel algorithms to execute in fewer passes. This is designed to not only increases processing speed, but to improve power efficiency as well, by allowing higher throughput with fewer accesses to offchip memory. Shader Model 5.0 supports larger and more flexible thread groups with 3D indexing, giving programmers improved control over the domain of defining their algorithms, and enabling additional throughput due to increased multi-threading in the GPU.
* Atomic Operation Support: This is a key feature of CPUs that programmers have been demanding for GPUs as well. Atomic operations enable the more efficient and accurate combination of operations that try to modify the same memory addresses. GPUs are capable of running thousands of threads or thread groups in parallel, and if two or more of these threads try to manipulate the same variable or access the same memory location, it could result in data corruption. Without atomic operations, programmers either had to modify their algorithms to avoid these situations, or otherwise serialize updates to shared variables or memory locations (effectively eliminating much of the performance benefit from parallel processing). Atomic operations allow these situations to be handled gracefully regardless of the number of parallel threads being executed, which helps maximize performance and simplify porting of algorithms from the CPU to the GPU.
* Gather4: Modern GPUs use dedicated hardware blocks known as texture units to fetch data rapidly into their processing cores. These texture units have historically been optimized for rendering graphics, where techniques such as bilinear filtering are typically used to improve image quality. Compute Shaders often make use of these same units to fetch data as well, but they generally have no use for their filtering capabilities, leaving them underutilized. GPUs with Shader Model 5.0 support have the ability to use the excess fetch capability with the Gather4 operation, which can fetch up to 4 values simultaneously and provide a 4xincrease in data bandwidth.
2. Improved Precision and Integer Processing: DirectX 11 enables support for double precision (64-bit) floating point operations on the GPU, according to the IEEE-754 standard. Until recently, this level of precision was only supported on CPUs, with GPUs being limited to single precision (32-bit) operations. While single precision is sufficient for most graphics applications, it can be insufficient for some simulation or number-crunching tasks that require large numbers of iterations on a single data value, or work with very large or very small values. Shader Model 5.0 also adds new integer and bit manipulation operations, such as count bits set, find first bit, insert/extract bit fields, reverse bits, and new bit shift operations. Applications such as video processing and cryptography use operations like these extensively, and can therefore benefit from improved performance on DirectX 11 GPUs.
3. Tight Integration between Compute Shaders and Rendering Pipeline: Although Compute Shaders are primarily intended to handle non-graphics tasks, they can often be used to enhance or interface with a rendering pipeline to influence what is sent to a display. Examples include simulation tasks, like game physics or artificial intelligence, that can control the movement or behavior of objects and characters that are drawn on-screen; sorting techniques, like order independent transparency, that optimize the rendering of large numbers of objects; and postprocessing effects, like tone mapping and depth of field, which can apply various filters to modify and enhance an image after it has finished rendering. DirectX 11 Compute Shaders share a common instruction set with other DirectX 11 shader types used for rendering (including Vertex, Hull, Domain, Geometry, and Pixel Shaders), and can share data structures to implement these techniques in a much more practical and efficient manner.
4. Improved Ease of Programming and more efficient memory usage: Powerful hardware is useless without software that can take advantage of the hardware’s capabilities. As a compute language, Shader Model 5.0 enables significant improvements that can enhance a programmer’s ability to model programs and algorithms for the GPU that were once impractical or impossible. By liberating development time from working around the restrictions of earlier GPU compute languages, the programmer’s imagination and energies can be focused instead on the actual compute problem. Shaders Model 5.0 adds some key features that make it easier to model and solve compute problems on the GPU, including:
* Increased Shared Memory with Improved Access: A key feature of DirectX 11 Compute Shaders is support for shared memory, which allows communication between threads. Shader Model 5.0 doubles the amount of shared memory available to a thread group, from 16 to 32 kilobytes. In addition to more shared memory, DirectX 11 class GPUs allow indexed reads and writes to this memory, whereas older DirectX 10 / 10.1 class GPUs limited access to private writes with shared reads. Allowing threads to directly read and write shared memory increases data parallelism within thread groups and simplifies porting of CPU code to run on the GPU. The combination of larger thread groups and more shared memory can also greatly reduce the number of non-local memory accesses required by some algorithms, which would reduce memory bandwidth requirements and improve performance.
* Append/Consume Buffers: Shader Model 5.0 supports a new type of data buffer that behaves like a stack or a list, instead of a fixed array of values. New data values are written to the end of the list as they are generated, or read from the end of the list as they are required. This is useful for implementing irregular data structures that require a different number of data values for each element, or for adaptive techniques like stream compaction that do a variable amount of processing for each element. Append buffers allow these processes to be performed in a single pass over the data, instead of requiring multiple passes which consume more memory bandwidth and compute cycles.
* Unordered Access Views (UAV): A UAV is a buffer that allows data to be written to or read from arbitrary locations, instead of a pre-defined order. Also known as “scatter/gather” operations, these add a great deal of flexibility that was not available in older GPUs. DirectX 11 extends this flexibility beyond what was possible with DirectX 10 class GPUs by allowing Compute Shaders to access up to 8 different UAVs at a time instead of just one. The DirectX 11 programming interface allows these UAVs to be accessed by Pixel Shaders as well, which facilitates data sharing between Compute Shaders and the rendering pipeline. These enhancements allow a variety of pre- and post-processing algorithms to be implemented more efficiently with DirectX 11 class GPUs.
* Indirect Compute Dispatch: This feature enables the generation of new workloads created by previous rendering or compute shading without CPU intervention. This further reduces CPU overhead and frees up more processing time to be used on other tasks.
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http://www.legitreviews.com/article/1001/1/
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[Legit]AMD DirectX 11 White Paper Released
06-26-09
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