More is less: Improving the energy efficiency of data movement via opportunistic use of sparse codes
More is less: Improving the energy efficiency of data movement via opportunistic use of sparse codes
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多即是少：通过机会性地使用稀疏代码来提高数据移动的能源效率
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
Engin Ipek
中科院分区：
文献类型：
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作者：
Yanwei Song;Engin Ipek
在长时间和高电容互连上的数据传输占纳米IC所消耗的能量的很大一部分。DDRx是采用最广泛的DRAM接口家族，在广泛的计算机系统中对整个系统的能量贡献很大。为了降低数据传输的能量成本，DDR4采用了伪开漏IO电路，该电路仅在发送或接收0时消耗功率，从而使IO能量与通过数据总线传输的0的数量成正比。因此，DDR4标准支持数据总线反转(DBI)编码技术，以使用少量0对每个字节进行编码。虽然比DBI更先进的稀疏编码技术可以进一步降低IO功率，但到目前为止，这些代码的相对较高的带宽开销阻碍了它们在DDRx总线上的应用。提出了一种建立在DDR4之上的新型数据通信框架MIL(More Is Less)，该框架利用DRAM时序限制导致的数据总线未充分利用来选择性地应用稀疏码，从而在不影响系统性能的情况下降低IO能量。在一组11个并行应用上的测试结果表明，在传统的DDR4系统上添加MIL可以使IO接口平均能量降低49%，DRAM系统平均能量降低8%，而性能平均下降不到2%。
Data movement over long and highly capacitive interconnects is responsible for a large fraction of the energy consumed in nanometer ICs. DDRx, the most broadly adopted family of DRAM interfaces, contributes significantly to the overall system energy in a wide range of computer systems. To reduce the energy cost of data transfers, DDR4 adopts a pseudo open-drain IO circuit that consumes power only when transmitting or receiving a 0, which makes the IO energy proportional to the number of 0s transferred over the data bus. A data bus invert (DBI) coding technique is therefore supported by the DDR4 standard to encode each byte using a small number of 0s. Although sparse coding techniques that are more advanced than DBI can reduce the IO power further, the relatively high bandwidth overhead of these codes has heretofore prevented their application to the DDRx bus. This paper presents MiL (More is Less), a novel data communication framework built on top of DDR4, which exploits the data bus under-utilization caused by DRAM timing constraints to selectively apply sparse codes, thereby reducing the IO energy without compromising system performance. Evaluation results on a set of eleven parallel applications show that MiL can reduce the average IO interface energy by 49%, and the average DRAM system energy by 8% when added on top of a conventional DDR4 system, with less than 2% performance degradation on average.