一种高性能北桥芯片的设计及性能分析

Design Implementation and Performance Analysis of a High Performance Northbridge

计算机系统整体性能的提高不仅仅依赖于处理器计算能力的提升也需要高性能芯片组的有力支持.芯片组承担着CPU和外围设备通信的重任,而且目前大多数系统中采用把内存控制器集成在北桥中的方法,这更加突出了北桥在访存性能以至于在整个系统中的关键作用.以高性能为目标,龙芯2C处理器配套北桥芯片NB2005的设计和优化采用了很多新的方法和技术,其中包括根据程序行为进行动态Page管理的内存控制电路,一种与内存控制电路状态相结合的预取策略和具备高吞吐量低延迟的PCI通道设计等.性能测试和分析表明,搭配NB2005的龙芯2C系统访存带宽要比搭配Marvell GT64240北桥的系统提高40%以上,运行SPECCPU2000浮点和定点程序的性能分别提高了12.2%和2.5%,磁盘I/O的性能也提高了30%.

To improve the performance of the entire computing system, not only the performance of CPU needs to be boosted, but also high performance chipsets are needed. Chipsets are responsible for data delivery between CPU and other devices, commonly with memory controllers embedded as crucial components, and this significance is highlighted as the memory access latency has become one of the most significant bottlenecks in nowadays computer systems. Discussed in this paper are the methods of designing and implementing a northbridge targeting at high performance. The architecture of NB2005--a northbridge for Godson-2 processor--and the optimization techniques applied on each module are described in detail. A novel dynamic page management strategy in DDR controller is proposed, which exploits the spatial locality characteristics of programs to reduce memory access latency. A new steam buffer mechanism is described, which at runtime jointly considers the memory access behavior and the status of memory controller. Also presented is a new buffer-swap mechanism implemented in PCI channel to improve the throughput of PCI bus. Experiments show that the Godson-2 system augmented with NB2005 outperforms that with Marvell GT64240 in all aspects tested. Specifically, NB2005 achieves above 40% memory bandwidth enhancement, yie also improves the lds speedups of 12.2 % and 2.5 % in SPEC INT2000 and SPEC FP2000 respectively and disk I/O performance by more than 30 %.