RDMA Metadata Timestamp Compression for One-Way Delay Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for clock synchronization between machines in data centers face limitations due to noise introduction by the OS stack and inefficiencies in timestamp transmission, leading to inaccurate OWD calculations and network congestion.
Innovation Solution
Utilizing RDMA to directly access system software timestamps and inject compressed timestamps into metadata fields of RDMA application-level messages for accurate OWD calculations, while employing netcam modules for congestion control and flow scheduling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If timestamps are added to packet headers or payloads, then clock synchronization accuracy is improved, but packet size increases causing network latency and MTU exceeded errors
Solution Approach 1:
The patent extracts the timestamp functionality from the traditional packet header/payload structure and relocates it to the RDMA descriptor metadata. This separation allows timestamps to be transmitted efficiently without increasing application packet size, as the descriptor metadata is handled by the RDMA subsystem rather than the application layer packet processing path.
Solution Approach 2:
The RDMA descriptor acts as an intermediary structure between the timestamp source and the packet. Instead of embedding timestamps directly in packet headers or payloads, the descriptor serves as a mediator that carries timestamp information independently, allowing efficient transmission without compromising packet integrity or increasing latency.
2Reliability
If timestamps are sent out-of-band separately, then timestamp transmission reliability is improved, but network overhead increases and timely arrival is not guaranteed
Solution Approach 1:
The patent merges timestamp transmission with the existing RDMA data flow by embedding timestamps in the descriptor metadata. This consolidation eliminates the need for separate out-of-band timestamp messages, reducing network overhead while maintaining reliability through the established RDMA connection.
Solution Approach 2:
The RDMA descriptor metadata serves multiple functions: it carries both the data payload information and the timestamp information. This multi-functionality eliminates the need for dedicated timestamp transmission channels, reducing overall network overhead while ensuring timely delivery through the same reliable RDMA path.
3Productivity
If NIC timestamps are used for synchronization, then hardware timestamping capability is improved, but host system clock synchronization accuracy deteriorates due to follower clock control and reading latency
Solution Approach 1:
The patent introduces the RDMA descriptor as an intermediary that carries timestamps from the sender's host clock directly to the receiver. This mediator bypasses the follower clock control mechanism inherent in NIC timestamps, allowing the receiver to access accurate sender timestamps without being constrained by the NIC's clock synchronization protocol or reading latency.
Solution Approach 2:
The patent replaces the mechanical NIC clock synchronization mechanism with a software-based RDMA descriptor approach. Instead of relying on hardware timestamping that ties the host clock to the NIC clock, the system uses RDMA to transfer software-generated timestamps directly, eliminating the follower clock constraint and reducing reading latency impacts.
4Ease of operation
If OS stack is used for timestamp transmission, then software timestamping is improved, but measurement precision deteriorates due to OS stack latency noise
Solution Approach 1:
The patent extracts the timestamp transmission path from the OS stack by using RDMA's direct memory access capability. This extraction removes the OS stack latency noise from the timestamp measurement path, allowing software timestamps to be generated and transmitted without passing through the OS networking stack that introduces variability and noise.
Solution Approach 2:
The patent replaces the OS stack-based timestamp transmission mechanism with RDMA's direct memory access system. This substitution eliminates the mechanical overhead of OS packet processing, context switches, and network stack handling that introduce latency noise, while maintaining software timestamping flexibility.
Data Source
AI summary
An application identifies a metadata field within a Remote Direct Memory Access (RDMA) message structure that can be used for timestamp injection. The application generates a high-resolution timestamp that captures a time when the RDMA message is sent, where the high-resolution timestamp has a first size that exceeds a size of the metadata field. The application compresses the high-resolution timestamp into a compressed timestamp having a second size that fits within the size of the metadata field, and injects the compressed timestamp into the metadata field of the RDMA message, the RDMA message sent from a sender host to a receiver host. The application calculates a one-way delay between the sender host and the receiver host using the compressed timestamp, and outputs a control signal based on the one-way delay.