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This paper presents a novel approach for monitoring disjunct, concurrent operations in heavily queued systems. A nonobtrusive activity monitor is used as an on-chip tracing unit. For each pending operation the monitor uses the hardware implementation of an event-triggered operation graph to trace the path of the operation through the system. In contrast to conventional tracing units, which collect and record information from one or more functional units for later analysis, the presented solution directly records the path taken by the operation through the system, making possible an immediate analysis of operation inconsistencies. For each followed path a unique signature is generated which significantly reduces the amount of trace data to be stored. The trace information is stored together with a time stamp for debugging and measuring of queueing effects and timing behavior in the system. The method presented has been successfully applied to the memory-bus adapter chips in the S/390® G5 a nd G6 systems.
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