Two processes bound to different cpu cores affect each other

I have two different processes A and B and they are bound to diffenrent cpu cores. A is bound to cpu cores: 0-4 and B is bound to cpu cores: 8-12.
After A's CPU usage is doubled, B's processing speed is slow.
When I kill A，the B's processing speed is fast.
If I kill A, and use stress-ng simulation A to stress test on CPU cores 0-4,B's processing speed is slow. What could be causing this problem? A and B are obviously running on different CPU cores.