Monitors

Chapter Seven

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Outline

• Monitors• Software monitors• Hardware monitors

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Monitors

• A monitor is a tool used to observe the activities on a system

• Useful for:– Software optimization– Finding bottlenecks– Tuning– Characterizing workloads

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Definitions

• Event is a change in the system state• Trace is a log of events usually including event

times• Monitors often have overheads

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Monitor types

• Triggers– Event driven: good for infrequent events– Timer driven (sampling): good for frequent events

• Results displaying– Online– Batch

• Implementation– Software, hardware, firmware, hybrid

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Software monitors

• Activation mechanism:– Trap instruction– Trace mode; interrupt after every instruction– Timer interrupt (resolution problem)

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Hardware monitors

• Probes• Counters• Timers• Logic analyzers

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Comparison

Criterion Hardware monitor

Software monitor

Domain HW events Application and OS events

Input rate High LowTime resolution High Low

Overhead None Varies

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