T-NBC:透明的MPI非阻塞集合操作

T-NBC: Transparent Non-blocking MPI Collective Operations

在不修改应用程序的前提下,在MPI通信库中将阻塞的集合操作转化为非阻塞的实现可以将集合通信与紧跟在集合操作之后的计算重叠起来,从而提高应用的性能.在应用中,集合操作之后的计算包括集合通信无关的计算和集合通信相关的计算两类.集合通信可以与前者很好地重叠;由于后者需要访问通信数据,与后者的重叠和集合通信中多个集合子消息的通信顺序密切相关.在该文中,我们实现了对应用透明的非阻塞集合操作T-NBC(Transparent Non-Blocking Collective operations).T-NBC不但将集合通信与集合通信无关的计算充分重叠起来,而且为了进一步增大集合通信与集合通信相关计算的重叠,它可根据应用访问多个集合子消息的顺序赋予这些子消息不同的通信优先级.微基准测试显示,T-NBC可以将绝大部分的集合通信与集合操作之后的计算重叠起来.在NPB(NAS Parallel Benchmarks)测试FT(Fourier Transform)和IS(Integer Sort)中,尽管集合操作之后的计算主要为集合通信相关的计算,但很大部分的集合通信时间被重叠,它们的性能分别提高了5%和36%.

Without modifying MPI applications,transparently translating MPI collective operations into non-blocking ones in communication libraries can overlap collective communication with the computation following the operations and benefit most current applications.In applications,the following computation includes communication-unrelated computation（CURC） and communication-related computation（CRC）.CURC is easier to overlap with collective communication;however,CRC need access communication data and is more difficult to overlap with collective communication.In the paper,we propose transparent non-blocking collective operations（T-NBC）.It can obtain the overlap between collective communication and following communication.Besides the overlap with CURC,it improves the overlap with CRC by transmitting collective messages with different priorities according to their accessed sequence in applications.Evaluations of micro-benchmark demonstrate that a large potential overlap between collective communication and following computation can be obtained.In FT（Fourier Transform） and IS（Integer Sort） of NPB（NAS Parallel Benchmarks）,even following computation dominated by CRC,a large portion of collective communication is overlapped.Their performance is respectively improved by 5% and 36%.