739c6df94e
The probe patch is motivated by the desire to move analytical and trace code away from functional code. This is achieved by the probe interface which is essentially a glorified observer model. What this means to users: * add a probe point and a "notify" call at the source of an "event" * add an isolated module, that is being used to carry out *your* analysis (e.g. generate a trace) * register that module as a probe listener Note: an example is given for reference in src/cpu/o3/simple_trace.[hh|cc] and src/cpu/SimpleTrace.py What is happening under the hood: * every SimObject maintains has a ProbeManager. * during initialization (src/python/m5/simulate.py) first regProbePoints and the regProbeListeners is called on each SimObject. this hooks up the probe point notify calls with the listeners. FAQs: Why did you develop probe points: * to remove trace, stats gathering, analytical code out of the functional code. * the belief that probes could be generically useful. What is a probe point: * a probe point is used to notify upon a given event (e.g. cpu commits an instruction) What is a probe listener: * a class that handles whatever the user wishes to do when they are notified about an event. What can be passed on notify: * probe points are templates, and so the user can generate probes that pass any type of argument (by const reference) to a listener. What relationships can be generated (1:1, 1:N, N:M etc): * there isn't a restriction. You can hook probe points and listeners up in a 1:1, 1:N, N:M relationship. They become useful when a number of modules listen to the same probe points. The idea being that you can add a small number of probes into the source code and develop a larger number of useful analysis modules that use information passed by the probes. Can you give examples: * adding a probe point to the cpu's commit method allows you to build a trace module (outputting assembler), you could re-use this to gather instruction distribution (arithmetic, load/store, conditional, control flow) stats. Why is the probe interface currently restricted to passing a const reference: * the desire, initially at least, is to allow an interface to observe functionality, but not to change functionality. * of course this can be subverted by const-casting. What is the performance impact of adding probes: * when nothing is actively listening to the probes they should have a relatively minor impact. Profiling has suggested even with a large number of probes (60) the impact of them (when not active) is very minimal (<1%). |
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SConscript | ||
simple_trace.cc | ||
simple_trace.hh | ||
SimpleTrace.py |