Remote Access Array for NUMA Lateral Snoop Reduction
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Solution Overview
Problem
In computer systems with a non-uniform memory access (NUMA) architecture, lateral snoops are frequent, leading to increased latency, bandwidth consumption, and reduced performance due to the need to investigate data across multiple nodes before accessing main memory.
Innovation Solution
Implementing a remote access array that tracks data portions moved across nodes, reducing the need for snoops by setting bits for accessed data lines and allowing immediate local memory access if the remote node does not have the data, thereby conserving bandwidth and power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lateral snoops are performed across multiple nodes to investigate data before accessing main memory, then data accuracy is ensured, but latency increases and bandwidth is consumed
Solution Approach 1:
The remote access array pre-records which data lines have been pulled to remote nodes before main memory access attempts. When a snoop is needed, the system checks this pre-recorded information to determine if the remote node actually has the data, avoiding unnecessary cross-node snoops and reducing latency while maintaining data accuracy through selective validation
Solution Approach 2:
The remote access array acts as an intermediary structure between main memory and remote nodes. It provides a lookup mechanism that mediates between the need for data accuracy (by identifying which remote nodes may have data) and the need for low latency (by avoiding unnecessary snoops), thus resolving the contradiction through an intermediate information layer
2Reliability
If lateral snoops are performed across multiple nodes to investigate data before accessing main memory, then data accuracy is ensured, but bandwidth consumption increases
Solution Approach 1:
The remote access array pre-records remote data pulls in advance, allowing the system to check this information before initiating snoops. This preliminary recording enables the system to avoid unnecessary bandwidth-consuming snoops to remote nodes that don't have the requested data, while still ensuring data accuracy by validating against the recorded information when needed
Solution Approach 2:
The remote access array serves as an intermediary that filters bandwidth consumption. By providing pre-recorded information about remote data locations, it mediates between the need for data accuracy (requiring some validation) and bandwidth conservation (avoiding unnecessary transmissions), allowing the system to make informed decisions about when snoops are actually necessary
3Loss of energy
If the remote access array is implemented in non-addressable memory region, then bandwidth and power are conserved, but access flexibility is reduced
Solution Approach 1:
The remote access array is placed in a non-addressable memory region specifically optimized for its tracking function. This local specialization allows the array to be implemented with simpler, more energy-efficient hardware designed solely for tracking remote data pulls, rather than requiring full-featured addressable memory. The trade-off in access flexibility is acceptable because the array only needs to perform specific tracking and lookup operations, not general-purpose memory access
Data Source
AI summary
A computer system and a method implementing a remote access array are provided. A first drawer includes a first processor chip. A first main memory region is operatively connected to the first processor chip. A first non-addressable memory region is operatively connected to the first processor chip and includes the first remote access array. The first remote access array is configured to track data portions that are stored in the first main memory region and for which copies were created and sent to an external node. The first remote access array is backed up in the first main memory region. The first remote access array includes one or more entries and is configured to update all of the entries in response to a multi-drawer working partition being reduced to fit within the first drawer.