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.

The emitters, selected on the GUI screen (Figure 1), de-couple performance event-collection from performance analysis tools. The emitter event-analysis system has two primary functions:

Event Data Production — During simulation, the simulator can identify a wide variety of architectural and programmatic events that influence system and software performance. Using configuration commands, you can request the simulator to emit records for a specific set of events into a circular, shared memory buffer. Reader programs attach to the shared memory buffer to consume these event records. Examples of emitter events include instruction execution, memory-reference addresses, and cache hits and misses.
Event Processing — There are one or more readers that analyze event records from this buffer. The readers typically compute performance measurements and statistics, visualize system and application behavior, and capture traces for post-processing. The simulator is prepackaged with a set of prebuilt sample emitter readers, and users can develop and customize their own emitter readers.

Figure 1 shows the emitter selections available by clicking the Emitters button on the GUI screen.

Figure 2 shows the emitter architecture. Emitters can be used in any simulator mode. The writer toggle buttons in the GUI are used to enable or disable production of the associated event to the circular buffer. An emitter reader program is needed to receive the events from the circular buffer using the emitter reader API.

The emitter framework is meant for programmers who wish to conduct performance analyses or capture traces by developing custom reader programs.

Figure 1. Emitters

Figure 2. Emitter architecture

The types of events that can be tracked are described in:

 /opt/ibm/systemsim-cell/include/emitter/emitter_data_t.h

The categories of events are:

Begin/end markers (Header, Footer)
PPU and SPU instructions
Cache hits or misses
Process/thread state (create, resume, kill, and so forth)
Translation Lookaside Buffer (TLB), Segment Lookaside Buffer (SLB), Effective-to-Real Address Translation (ERAT) operations
Device operations (disk)
Annotations
Transactions