Gist

The gist system can be used in any C program running on a Butterfly GP-1000 or TC-2000. It provides C macros by which a user can instrument his program to log whatever events he chooses. Events are logged to local memory on each processor, time-stamped with the value of the Butterfly's microsecond timer, and only written to disk at the end of the run. One can think of them as then sorted by time to produce a log file of events in proper sequence. This mechanism provides efficient logging at the expense of memory usage. Indeed, it may be necessary to log events sparsely or else restrict oneself to short runs, in order to avoid the memory restrictions imposed by this implementation.

The log file is displayed statically, with a time line for each processor, showing the various types of events as numbered boxes on the line. It is also possible to define states of a process by entry and exit events, and display statistical information about state durations. The display can be scrolled backward and forward in time, and magnified for close examination of the event sequence. The implementation is based on X-windows. The gist program is only implemented on the Butterly itself.