BTB索引散列算法的研究与设计

发布时间：2018-02-25 01:23

  本文关键词： 分支目标缓冲 散列索引 XOR散列函数 分支目标地址预测 分支预测　出处：《计算机研究与发展》2014年09期 　论文类型：期刊论文

【摘要】：分支误预测是影响高性能处理器性能进一步提升的一个主要因素.现代处理器采用分支目标缓存(branch target buffer,BTB)预测分支指令的目标地址,BTB的预测精度受限于其命中率.由于程序中分支指令的分布并不均匀,传统的BTB索引方式无法充分利用BTB资源,从而造成不必要的冲突缺失,影响分支目标地址的预测精度,采用散列索引方式优化访问映射关系是有效解决方法之一.当前大量文献研究了cache的访问方式,但对BTB的散列索引算法的专门探讨则显不足.为了消除分支指令的分布空洞,离散分支指令和BTB条目的固有映射关系,设计了用于BTB索引的XOR散列算法和优化的bit-select索引算法,使用概率方法对BTB单组最大映射数期望的上界作了估计,并对这两种散列索引算法的效果进行了模拟评估.实验结果表明,散列映射方式能够较好地避免BTB冲突缺失造成的预测失败,XOR散列算法的离散效果更好.
[Abstract]:Branch error prediction (BTB) is one of the main factors that affect the performance of high performance processors. In modern processors, the accuracy of BTB prediction for branch instruction is limited by its hit ratio. Because of the uneven distribution of branch instructions in the program, Traditional BTB indexing method can not make full use of BTB resources, which causes unnecessary conflicts and affects the accuracy of branch target address prediction. Using hash index to optimize access mapping is one of the effective methods to solve this problem. A large number of literatures have studied the access mode of cache, but the special discussion of BTB's hash index algorithm is insufficient. Based on the inherent mapping relationship between discrete branch instructions and BTB items, a XOR hash algorithm for BTB index and an optimized bit-select index algorithm are designed. The upper bound of the expected maximum number of BTB maps is estimated by using the probability method. The experimental results show that the Hash mapping method can avoid the prediction failure caused by the BTB collision loss and the XOR hash algorithm has better discretization effect.
【作者单位】： 国家高性能集成电路设计中心;
【基金】：“核高基”国家科技重大专项基金项目(2009ZX01028-002-001)
【分类号】：TP332
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本文编号：1532484