Users access the x86 quantization backend by default for x86 platforms, and the selection between different kernels is automatically done behind the scenes. The rules of selection are based on prior performance testing data done by Intel during feature development. Thus, the x86 backend replaces FBGEMM and may offer better performance, depending on the use case.
The selection rules are:

On platforms without VNNI (e.g., Intel® Core™ i7 processors), FBGEMM is always used.
On platforms with VNNI (e.g., 2nd-4th Gen Intel® Xeon® Scalable processors and future platforms):
For linear, FBGEMM is always used.
For convolution layers, FBGEMM is used for depth-wise convolution whose layers > 100; otherwise, oneDNN is used.



Note that as the kernels continue to evolve.