CSR: III: CGV: Medium: Architectures for Energy Efficient Ray Tracing

计算机图形学已经成为几乎所有现代计算设备的一个组成部分。这些机器的范围从高性能系统、科学工作站和台式计算机，到专用游戏控制台，以及移动电子设备，如笔记本电脑、平板电脑和电话。所有这些设备都有专用的加速器，可以实现高性能的3D图形。然而，这些被称为图形处理单元（gpu）的加速器正受到功耗和相关热问题的限制。随着芯片迁移到新工艺，工艺技术的改进可以帮助降低能耗，但在计算机图形学中，场景复杂性和对图像质量的新要求不断增加。这对GPU提出了新的要求，并且无论GPU是部署在桌面工作站还是能源受限的移动平台上，都要保持高功率/热包络。该项目旨在通过开发新算法和新架构来解决这个问题，以实现高度逼真的3D计算机图形图像合成，其功耗明显低于当前GPU的增长趋势。这项工作的目标是光线追踪作为一种渲染算法。光线追踪在支持高质量合成全局照明效果的逼真渲染方面具有众所周知的优势。它也非常适合并行处理，尽管利用不同类型的并行性比目前的商用gpu提供。光线追踪也可以自然地调节图像质量给定实时时间或能量限制。这对于当前商用gpu使用的基于z缓冲区的渲染技术来说要困难得多。从一个经过验证的框架开始，该框架具有轻量级的多指令多数据（MIMD）线程处理器，可以很好地处理单指令多数据（SIMD）包中无法高效执行的计算，该计划是同时开发新的体系结构和新算法，它们将协同工作，以更低的能源成本生成图像。预计整个项目的主要贡献包括：详细检查渲染具有各种照明效果的图像所需的能量；通过光线节流和硬件辅助的无帧渲染技术来权衡图像质量、能量和渲染速度的技术；内存系统增强，减少数据移动和相关的能源成本；在光线追踪算法的许多部分中，我们最近在数据流和运行时管道重新配置方面的工作的新扩展；利用我们定制架构的算法改进。如果成功，这项工作有可能从根本上改变计算机图形传递给大量终端用户的方式。提高图像质量和降低能耗的承诺可能会改变我们在未来计算设备上体验图形的方式。

Computer graphics have become an integral part of nearly all modern computing devices. These machines range from high-performance systems, scientific workstations, and desktop computers, to dedicated gaming consoles, and to mobile electronics such as laptops, tablets, and phones. All of these devices have dedicated accelerators that enable high-performance 3D graphics. However, these accelerators, known as graphics processing units - GPUs, are becoming limited by power consumption and associated thermal issues. Improvements in process technology can help reduce energy requirements as chips migrate to the new processes, but in computer graphics, scene complexity and new demands for image quality are ever increasing. This places new demands on the GPU, and conspires to keep the power/thermal envelope high regardless of whether the GPUs are deployed in desktop workstations or energy constrained mobile platforms. This project aims to address this problem by developing new algorithms and new architectures for highly realistic 3D computer graphic image synthesis that consume significantly less power than current GPU growth trends.This work is to target ray tracing as a rendering algorithm. Ray tracing has well-understood advantages in supporting realistic rendering with high quality composite global lighting effects. It is also highly amenable to parallel processing, albeit utilizing a different type of parallelism than offered by current commercial GPUs. Ray tracing can also be naturally throttled to adjust the image quality given real-time temporal or energy constraints. This is much more difficult with the Z-buffer based rendering techniques used by current commercial GPUs. Starting from a proven framework with lightweight multiple-instruction, multiple-data (MIMD) thread processors that perform well with computations that are not efficiently executed in single-instruction, multiple-data (SIMD) bundles, the plan is to simultaneously develop new architectures and new algorithms that will work together to produce images with a lower energy cost.Expected primary contributions of the overall project include: a detailed examination of the energy required to render images with various lighting effects; techniques for trading off image quality, energy, and rendering speed through ray throttling and hardware-assisted frameless rending techniques; memory system enhancements to reduce data movement and the associated energy cost; novel extensions of our recent work in data streaming and runtime pipeline reconfiguration in many parts of the ray tracing algorithm; algorithmic improvements that take advantage of our custom architecture. If successful, this work has the potential to change fundamentally the way that computer graphics is delivered to a huge variety of end users. The promise of improved image quality and lower energy costs could change the way we experience graphics on future computing devices.