RDMA Message Pacing With Local Timers to Reduce Latency

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Solution Overview

Problem

Conventional RDMA systems suffer from inefficiencies and unreliability due to unsynchronized data operations, incomplete transmissions, retransmissions, and high latency caused by limited network interface controllers, fence flags, and unsynchronized flow control, leading to increased latency and degraded performance.

Innovation Solution

Implementing a sending device with a local pacing timer to manage the transmission of RDMA messages, allowing for timed pacing and congestion control, ensuring synchronized operations and reducing latency by transmitting messages based on predefined timer durations and network conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional RDMA technique synchronizes events to maintain specific order of execution, then data communication reliability is improved, but transmission latency increases and throughput decreases

Engineering Contradiction:

Improvedata communication reliabilityVSAvoidtransmission latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The sending device transmits a hint message before the actual data message to preliminarily notify the receiving device of upcoming data transmission. This allows the receiving device to prepare its buffers and resources in advance, enabling faster processing when the actual data arrives, thus reducing overall transmission latency while maintaining reliability through the preliminary notification mechanism.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The hint message acts as an intermediary between the sending and receiving devices, carrying preliminary transmission information without requiring immediate acknowledgment or synchronization. This intermediary mechanism decouples the strict event synchronization requirements, allowing data transmission to proceed with reduced latency while the receiving device can process the hint independently and prepare accordingly.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If conventional RDMA technique uses fences to enforce in-order execution, then execution order is maintained, but total execution time significantly increases

Engineering Contradiction:

Improveexecution order stabilityVSAvoidtotal execution time

Core Design Contradiction:

Stability of the object's compositionVSDuration of action of moving object

Solution Approach 1:

The hint message is transmitted in advance to preliminarily establish the execution context and notify the receiving device of upcoming operations. This preliminary action allows the receiving device to prepare its execution environment without waiting for the actual data message, thereby maintaining proper execution order while significantly reducing the total execution time by eliminating idle waiting periods associated with traditional fence mechanisms.

Inventive Principle:

Principle #10Preliminary action

3Productivity

If conventional RDMA technique transmits data before previous operations complete, then throughput increases, but data communication reliability decreases

Engineering Contradiction:

Improvedata throughputVSAvoiddata communication reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The sending device transmits a hint message before the actual data message to preliminarily notify the receiving device of upcoming transmission. This preliminary notification allows the receiving device to prepare its buffers and validation mechanisms in advance, enabling it to process the actual data message more efficiently and reliably when it arrives, thus maintaining data communication reliability while improving throughput through reduced processing delays.

Inventive Principle:

Principle #10Preliminary action

4Device complexity

If network interface controllers have limited cache size, then device complexity is reduced, but information fetching from host memory increases latency

Engineering Contradiction:

Improvenetwork interface controller complexityVSAvoidinformation fetching latency

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The hint message is transmitted in advance to preliminarily notify the receiving device of upcoming data transmission. This allows the receiving device to fetch required information from host memory and prepare buffers before the actual data arrives, thereby reducing the latency impact of limited cache size while maintaining simple network interface controller design. The preliminary action shifts the timing of information fetching to occur during the interval between hint and data message reception.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP4122186B1Device and method for reducing latency in remote direct memory access system

Publication Date: 2025.10.22 HUAWEI TECH CO LTD

Figure 1
Figure 2A
Figure 2B

AI summary

In order to reduce latency in RDMA systems, a local timer is used to distribute messages being sent in time so that necessary preceding operations are allowed to complete before sending a new operation or command. Especially useful for RDMA systems when sending prefetch commands. FIG.2A