  XGC (X-point Gyrokinetic Code) is a whole-volume, total-f gyrokinetic
particle-in-cell code developed for modelling tokamaks. In recent work, XGC has
been extended to model more general 3D toroidal magnetic configurations, such
as stellarators. These improvements have resulted in the XGC-S version. In this
paper, XGC-S is benchmarked for linear electrostatic ion temperature
gradient-driven microinstabilities, which can underlie turbulent transport in
stellarators. An initial benchmark of XGC-S in tokamak geometry shows good
agreement with the XGC1, ORB5, and global GENE codes. A benchmark between XGC-S
and the EUTERPE global gyrokinetic code for stellarators has also been
performed, this time in geometry of the optimised stellarator Wendelstein 7-X.
Good agreement has been found for the mode number spectrum, mode structure, and
growth rate.
