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CS2410: Computer Architecture
Microarchitecture simulation issues
Sangyeun Cho
Dept. of Computer Science
University of Pittsburgh
Why microarchitecture simulation?
Arbitrary level of details and precision
•Pipelines, branch predictors, caches, main memory, …
•Novel microarchitectural ideas
•Hardware devices (e.g., hard drive, timer, …)
Full observability
CS2410: Computer Architecture University of Pittsburgh
Challenges
•Modeling time
•Validation
•Simulation time (speed)
If you have an idea to check, you may want to perform “proof-of-concept”
experiments before undertaking full microarchitecture modeling for
simulations
– E.g., collect necessary trace from program execution and process trace data
Full system simulator?
Widely used microarchitecture simulators, such as
SimpleScalar, use user-code-only simulation
•They do not simulate OS codes
•Some of them have a proxy call mechanism (to get help from the host
OS on a simulated program’s system calls)
CS2410: Computer Architecture University of Pittsburgh
Full system simulator provides a view of a more realistic
machine so that a native OS can be booted
•OS codes are actually simulated
Accuracy?
Function vs. timing simulation
Functional simulation
•Captures and simulates basic instruction semantics
•Updates processor states (register, memory, …)
•Generates correct program output
CS2410: Computer Architecture University of Pittsburgh
Timing simulation
•(Typically) performs functional simulation
•Implements various microarchitectural structures
•Captures the timing of events to obtain program execution time
Functional simulation takes less time
