schedsi - a scheduling simulator

This tool generates scheduling charts given scheduling algorithms and some threads.

Since I'm working on a hierarchical operating system, hierarchical scheduling is of interest to me,
this tool supports building process hierarchies and stacking schedulers along that hierarchy.
Each process, referred to as `Module`, has its own scheduler, which gets executed by a `VCPUThread` of the parent.
A single scheduler taking care of a bunch of threads is easily done by just using a single `Module` owning all threads.

The graph gets written as a SVG and to present hierarchical scheduling they are not in the usual Gantt chart where time is on the horizontal axis and the threads have fixed positions on the vertical axis.
Time still flows horizontally, but the vertical axis represents the depth of the hierarchy. Threads can be differentiated by their ID written on the bar.
Context switches are also modeled to take time (though it can be set to 0) and are also drawn as triangles going up or down the vertical axis.

There are five examples in `examples/`.
`examples/singletimer_kernel.py` and `examples/localtimer_kernel.py` describe the same process hierarchy and only differ in their hierarchical scheduling strategy, with the former using a single scheduling timer and the latter a per-module local timer.
There are two very similar examples in `examples/`, the only difference is the usage of either a single scheduling timer or per-module local timers.
`examples/penalty_scheduler.py` provides a variation that uses the penalty scheduler addon, as well as the MLFQ scheduler on the single scheduler timer strategy.
Finally there are two examples showcasing the CFS scheduler: `examples/cfs.py`, which uses the local timer stragegy and `examples/penalty_cfs.py`, which uses the penalty scheduler addon.

The example scripts produce a binary log file (MessagePack). To get a human readable version of the log `./replay.py` can be used to convert it to either a text log or a SVG graph. There are also various make targets to directly produce these logs from the examples.
The text log also prints statistics. Thread statistics are in JSON and histograms of it can be plotted using `./plot.py`. `./plot.py` can also parse binary log files for the statistics.
The `replay` and `plot` tools are installed as `schedsi-replay` and `schedsi-plot` by the `./setup.py` file (or the `install` make target).

`./HACKING` provides an overview of the inner workings.