PX4 controller sampling time

Hi everyone ,
I’m working in SITL and I noticed that the sampling time for controllers (rate) is set at 0.004s (250Hz).
Looking at the documentation I’ve seen that the frequency can be much higher. Someone can help me to understand which are the parameters to tune for having at least 1 khz?
I’ve tried to change the IMU_GYRO_RATE but nothing changed, i have to modify some parameters in gazebo?