Is my hiit training proper?

i do this on a treadmill 3 times a week i start off running 4 mph as a warmup then i increase it to 8mph and do this for a minute then drop it down to 3mph then i bring it up to 8mph again and drop down 3 mph again u get the point. Could anyone tell me if i am doin anything wrong and give me solutions if needed and dont give me any crap answers referring to heart rate i dont use dat **** just tell me how the speed should vary every minute.