Explain how to get process from context id better

[eero-t]

Currently gputop-ui lists just context ID, so user doesn't know which process he's actually monitoring. It should list also process name/PID (PID in case there are multiple processes with same name).

User needs debugfs, root and this to see what the contexts actually are:
# grep context /sys/kernel/debug/dri/0/i915_context_status

Related to #179.

[djdeath]

If you enable the default tracepoints from the initial window, gputop will use the tracepoint information to infer the process name/id from the context id based on who emitted what.

Eventually we want to have the i915 driver to do that work for us so that information is captured at submission rather after the fact (when the process might have died already).

[eero-t]

So it seems. I think GUI should indicate that somehow.

E.g. in "Select contexts" pop up a text saying "select default tracepoints to see process names".