This paper describes that data centers gradually adopt Remote Direct Memory Access(RDMA)technology to fulfill high-throughput and low-latency communication requirements.In an IP-based routing network,RDMA uses the RoCEv2(RDMA over Converged Ethernet version 2)protocol,which is based on Priority-based Flow Control(PFC)to ensure zero packet loss.However,with the triggering of the PFC mechanism,one of the serious problems called head-of-line blocking inevitably occurs and many innocent flows will be blocked.Existing methods use flow control and congestion control methods,so that the innocent flows can quickly recover the original sending speed after the congestion.However,the transmission of the innocent flows almost stagnate during the blocking period.The flow control time(FCT)of victim flows grows linearly with the congestion duration.To alleviate this problem,this paper introduces the xPFC(extended PFC),an extended PFC protocol based on traditional PFC protocol.Our design applies transient and dynamic flow priority shift mechanism to decouple the victim flows fromthe congested flows.Therefore,the victim flows can pass the congested port even during the congestion period.Our plenty of packet-level simulations verify that our design can effectively alleviate victim flows and the FCT of victim flows increases by less than 10 percent of the congestion duration.
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