LinuxConf Europe 2007

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Kernel Summit 2007

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Hiroyuki Machida - Sony, Akira Tsuakmoto - SCEI, Kuniyasu Suzaki - AIST

SPE-assisted User Level Device Driver on Linux for Cell/PS3

Cell broadband engine is a heterogeneous multi-core processor which consists of a Power PC element, (PPE) and 8 Synergic Processor Elements (SPEs).

SPE is a general purpose SIMD processor which is connected with 256KB local storage, (LS) instead of primary cache. SPE doesn't have access to main memory directly. Instead, SPE has a high-performance memory flow controller (MFC) which is able to transfer data between LS of different SPEs, and between main memory and LS. Due to this memory model, Cell BE can achieve very high performance, but it's necessary to rewrite conventional programs to utilise SPEs. If common services are accelerated by SPEs, conventional programs can enjoy the benefit of Cell BE without any modification.

This paper proposes utilizing SPEs from user space to accelerate kernel services to provide benefits of Cell BE to conventional programs. Our solution allows kernel services to access to multiple SPEs easily. We implemented this concept on PS 3 Linux. During this work, we modified compressed loop device driver, CLOOP and enhanced user level I/O device driver, UIO. We'll show evaluation of the concept and how it can achieve better performance than the conventional PC in most cases.

Through this experiment, we realized DMA transfers between main memory and local storage have big impacts on the entire system performance. We'll propose kernel function improvements to reduce these impacts and show how they work. We'll also discuss other programming tips and issues around SPEs to achieve better performance, possible other kernel services to be accelerated by SPEs, and a framework using enhanced UIO.

Submitted paper

Paper (PDF) and Paper (tgz) .