Core Concepts
Optimizing performance models for AMD's Zen+ CPUs without relying on per-port performance counters.
Abstract
The content discusses the development of a port mapping inference algorithm for AMD's Zen+ architectures, focusing on optimizing performance models without the need for per-port performance counters. The algorithm is based on a formal port mapping model and utilizes throughput measurements to infer port mappings accurately. It addresses challenges with measuring µops and identifies blocking instruction candidates, filtering out equivalent ones to ensure accurate results.
- Introduction:
- Understanding the importance of architecture performance characteristics.
- Models for exploiting instruction-level parallelism in out-of-order processors.
- Challenges in inferring port mappings due to lack of hardware support from manufacturers.
- Background:
- Overview of modern microarchitectures and their complex designs.
- Explanation of out-of-order execution and µop decomposition.
- Illustration of a simplified modern processor design.
- Data Extraction:
- "Recent Intel Core architectures support this, and AMD’s Zen, Zen+, and Zen2 are documented to support this as well."
- "Golden Cove has a UOPS_EXECUTED.THREAD performance counter."
- "Fujitsu’s A64FX microarchitecture provides a UOP_SPEC performance counter."
- "ARM’s Neoverse V2 uses an OP_RETIRED counter."
- "Apple’s M1 uses an undocumented performance counter."
- Case Study - AMD Zen+ Architecture:
- Evaluation of the port mapping inference algorithm with the AMD Zen+ microarchitecture.
- Comparison with existing documentation and tools like PMEvo and Palmed.
- Identification of unexpected behavior in macro-op to µop correspondence.
- Inquiry and Critical Thinking:
How can the algorithm adapt to handle pipeline bottlenecks in modern processors?
What implications does the discrepancy between observed µops and documented macro-op counts have on performance modeling?
How might advancements in hardware counters impact future iterations of the port mapping inference algorithm?
Stats
"Recent Intel Core architectures support this, and AMD’s Zen, Zen+, and Zen2 are documented to support this as well."
"Golden Cove has a UOPS_EXECUTED.THREAD performance counter."
"Fujitsu’s A64FX microarchitecture provides a UOP_SPEC performance counter."
"ARM’s Neoverse V2 uses an OP_RETIRED counter."
"Apple’s M1 uses an undocumented performance counter."