RDMA Latency Reduction via Intermediate Buffer Staging
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Solution Overview
Problem
The existing Remote Direct Memory Access (RDMA) protocol introduces latency due to the need for registration and deregistration of application memory buffers, which delays information transfer as the operating system kernel may move data to virtual memory, corrupting the transfer process and requiring buffer registration to prevent this.
Innovation Solution
The solution involves using intermediate buffers during registration and deregistration to overlap these processes, allowing information transfer to continue without waiting for completion, and optimizing the amount of data transferred during these phases by using blocks of increasing size and offset-based transfers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If application memory buffer is registered to prevent OS kernel from moving data, then data transfer reliability is improved, but latency increases due to registration/deregistration overhead
Solution Approach 1:
The system performs preliminary actions by pre-registering memory buffers and pre-positioning data before the actual RDMA transfer is needed. The application buffer is registered in advance with the RDMA device, and data is prepared in the buffer beforehand, so that when transfer is initiated, the operation can proceed immediately without registration overhead or OS intervention during the critical transfer window.
Solution Approach 2:
The invention extracts the registration and data preparation operations from the critical transfer path. By separating the buffer registration phase from the data transfer phase, and by using dedicated RDMA memory regions that are registered once and reused, the system removes the repetitive registration/deregistration overhead from each transfer operation, thereby reducing latency while maintaining reliability.
2Adaptability or versatility
If OS kernel moves data to virtual memory, then memory management flexibility is improved, but data corruption risk increases during RDMA transfer
Solution Approach 1:
The system segments memory into distinct regions: application buffers for user-space data, RDMA memory regions for direct RDMA access, and intermediate buffers for data staging. This segmentation allows the OS to manage virtual memory flexibly in the application buffer region while the RDMA memory region is explicitly pinned and registered with the RDMA device, preventing the OS from moving or swapping its contents during transfer operations.
Solution Approach 2:
The invention introduces intermediate buffers as a mediator between the application buffer and the RDMA memory region. Data is first copied to the intermediate buffer (which is registered with the RDMA device), and then the RDMA operation transfers it to the destination. This intermediate staging area acts as a buffer zone that isolates the RDMA transfer from OS memory management activities, ensuring data integrity while preserving memory management flexibility in the application layer.
Data Source
AI summary
The present disclosure provides systems and methods for remote direct memory access (RDMA) with reduced latency. RDMA allows information to be transferred directly between memory buffers in networked devices without the need for substantial processing. While RDMA requires registration/deregistration for buffers that are not already preregistered, RDMA with reduced latency transfers information to intermediate buffers during registration/deregistration, utilizing time that would have ordinarily been wasted waiting for these processes to complete, and reducing the amount of information to transfer while the source buffer is registered. In this way the RDMA transaction may be completed more quickly. RDMA with reduced latency may be employed to expedite various information transactions. For example, RMDA with reduced latency may be utilized to stream information within a device, or may be used to transfer information for an information source external to the device directly to an application buffer.