Performance monitoring

The simulator provides both functional-only and cycle-accurate simulation modes.

The functional-only mode models the effects of instructions, without accurately modeling the time required to execute the instructions. In functional-only mode, a fixed latency is assigned to each instruction; the latency can be arbitrarily altered by the user. Since latency is fixed, it does not account for processor implementation and resource conflict effects that cause instruction latencies to vary. Functional-only mode assumes that memory accesses are synchronous and instantaneous. This mode is useful for software development and debugging, when a precise measure of execution time is not required.

The cycle-accurate mode models not only functional accuracy but also timing. It considers internal execution and timing policies as well as the mechanisms of system components, such as arbiters, queues, and pipelines. Operations may take several cycles to complete, accounting for both processing time and resource constraints.

In the cycle-accurate mode, the simulator automatically collects many performance statistics. Some of the more important SPE statistics are:

• Total cycle count
• Count of branch instructions
• Count of branches taken
• Count of branches not taken
• Count of branch-hint instructions
• Count of branch-hints taken
• Contention for an SPE's local store
• Stall cycles due to dependencies on various pipelines

1. Displaying performance statistics
   You can collect and display simple performance statistics on a program without performing any instrumentation of the program code. Collection of more complex statistics requires program instrumentation.
2. SPE performance profile checkpoints
   The simulator can automatically capture system-wide performance statistics that are useful in determining the sources of performance degradation, such as channel stalls and instruction-scheduling problems.
3. Example program: tpa1
   The following example program tpa1 is used in the sections above to show the basic performance statistics that can be collected and displayed without instrumentation of the code.
4. Emitters
   In addition to the basic cycle-count and summary statistics provided by its profile checkpoints and triggers, the simulator also supports a user-extensible event-analysis system, called emitters.