Active Messages Using Selective Interrupts without Polling

Active Messages form a user-level communication mechanism that allows a message to extract itself from the network upon arrival at its destination. Delivery of such a message can be realized via an interrupt-driven or a polling-based approach. This paper proposes a new mechanism, Active Messages Using Selective Interrupts Without Polling (AM_SIWOP). It improves upon Active Messages by reducing the number of interrupt dispatch and deeply overlapping communication with computation. The AM_SIWOP uses dual hardware switched receive buffers and an adaptive timer in the network interface. Instead of each message causing an interrupt, a group of messages in a buffer as a whole will cause a single interrupt when the buffer becomes full or when a certain period of time has elapsed for messages waiting in a buffer. The timer is adjustable according to the communication traffic. The simulation results showed that the AM_SIWOP significantly improved the computational efficiency of Active Messages. In an AM_SIWOP with a pair of small buffers, messages would be delayed slightly when messages were arriving quickly. Due to the adaptive timer, communication latency of a message was bounded in light communication traffic. Since message buffering deepens the transmission pipeline of active messages, the AM_SIWOP increases the bandwidth of user-level communication.