This should be useful to visualize system-wide events in the CPU
timeline, especially once we add some more events.
We may want to define some modes eventually, as not all captures will
care about GPU visualization. However, it's pretty low overhead (60Hz
* number of monitors), so maybe we can just filter it out at
We do a bit more setup work than necessary here (looking up the config
number for the tracepoint per CPU, rather than looking it up once at
startup), but I suspect I'll want to refactor the init anyway once we
add more tracepoint markers.