Global GSPGPU_GetPerfLog (GSPGPU_PerfLog *outPerfLog)

The official sysmodule doesn't handle the PDC0/1 entries correctly after init. On the first frame GSPGPU_SetPerfLogMode is enabled, "last duration" will have a nonsensical value; and "total duration" stays nonsensical. This isn't much of a problem, except for the first frame, because "total duration" is not supposed to be used as-is (you are supposed to take the difference of this field between two time points of your choosing, instead).

Since it is running at approx. 3.25 GiB/s per bank, some small PSC operations might complete before the official GSP has time to record the start time.

The official sysmodule doesn't properly handle data synchronization for the perflog, in practice this should be fine, however.

Global GSPGPU_SetPerfLogMode (bool enabled)

The official sysmodule forgets to clear the "start tick" states to 0, though this should not be much of an issue (as per the note above).