Access Control Logic Table for Virtual Device Latency
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Solution Overview
Problem
In virtualization environments, handling access requests to virtual devices often results in significant performance overhead due to the need for exceptions and virtual device handling, which increases latency and reduces system performance.
Innovation Solution
A data processing apparatus with access control logic that references a table of address ranges and associated actions to handle access requests, allowing predicted accesses to be handled without exceptions, thereby improving performance by avoiding the overhead of exception handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If access requests to virtual devices are handled using exceptions and virtual device handlers, then virtual device functionality is properly emulated, but performance overhead increases significantly and latency increases
Solution Approach 1:
The patent applies preliminary action by pre-establishing a table of address ranges and associated actions before access requests occur. The access control logic proactively configures this table to map virtual device address ranges to appropriate handling actions, enabling predicted accesses to be handled directly without exceptions. This eliminates the need for exception handling overhead while maintaining proper virtual device emulation, thereby resolving the contradiction between reliability and productivity.
2Speed
If memory mapped virtual devices are accessed directly without exceptions, then access speed improves, but the system cannot handle registers that change upon repeated accesses and cannot implement side effects
Solution Approach 1:
The patent applies dynamics by implementing a configurable access control system that can adapt its behavior based on the specific address range and associated action defined in the table. The system dynamically determines whether to allow direct access, generate exceptions, or perform other actions based on the pre-configured table entries. This enables the system to maintain fast direct access for predictable patterns while retaining the ability to handle dynamic register changes and side effects when necessary, thus resolving the contradiction between speed and adaptability.
3Productivity
If a table of address ranges and actions is referenced for each access request, then predicted accesses can be handled without exceptions, but additional lookup operation is required
Solution Approach 1:
The patent applies segmentation by dividing the memory address space into discrete address ranges, each with its own associated action defined in the table. This segmentation allows the access control logic to efficiently lookup and apply the appropriate handling action for each address range without requiring complex analysis of the entire address space. By segmenting the address space into manageable ranges with pre-defined actions, the system achieves fast lookup and direct handling for predicted accesses while maintaining manageable complexity, thus resolving the contradiction between productivity and device complexity.
Data Source
AI summary
A data processing apparatus is provided comprising processing logic for issuing access requests when access to data is required, with each access request specifying a memory address associated with the data the subject of the access request. Access control logic is used to perform an access control operation to check for each access request whether the specified memory address is accessible by the processing logic. Further, a table is provided having a plurality of entries, each entry identifying an address range and an associated action. On occurrence of one or more predetermined events, the access control logic references the table to determine whether the specified address is within the address range identified by an entry of the table. If so, the associated action specified in that entry is invoked, whereas otherwise the access control logic causes any action indicated by the access control operation to be performed. This provides a particularly efficient mechanism for handling access requests in a variety of situations, for example within a virtualization environment where the access requests are directed to virtual devices implemented by hypervisor software.