jit and trt are two different things.
our team are looking into pytorch for a long time. jit is front-end while trt is back-end.
Always, jit is from python. it optimizes pytorch codes and tries to merge some  ops before running the forward. If you dig it, you will find jit and eager call the same op set and just little diff.
However, trt is another accelerated engine, which depends on Nvidia’s GPU. trt will fuse the ops as possible as it can. fused kernel can reduce cost of discrete kernel calls.
besides, trt has other exiting features.