You only use at most a “-j#” of the same number of cpu cores available. By default this is 4…with jetson_clocks.sh or nvpmodel you can crank it up to 6 cores because then the Denver cores kick in. So at absolute most you’d use “-j6”…just “-j4” if you didn’t enable all 6 cores.
I don’t know why only one core would be used under “-j9”, but perhaps if you specify more threads than cores it reverts back to a single core…or perhaps it detects running low on RAM with too many concurrent threads…I have not tested.
Because CPU0 is critical for hardware I/O I typically use “-j5”.
FYI, since only Image is used, and not a compressed zImage, you can just “make Image” and skip the extra disk space and time of compressing this.
make -j6 Image