The reason the time of the test and set code increases roughly linearly as the number of processors executing the critical section increases is because the test and set process doesn't do anything to prevent processors from competing over the lock despite the fact that inevitably only one processor will successfully acquire the lock. So, because only one processor can acquire the lock but all others will be spinning and attempting to acquire the lock there will be a constant large amount of competition around the lock, meaning there is a ton of bus traffic.
The reason the time of the test and set code increases roughly linearly as the number of processors executing the critical section increases is because the test and set process doesn't do anything to prevent processors from competing over the lock despite the fact that inevitably only one processor will successfully acquire the lock. So, because only one processor can acquire the lock but all others will be spinning and attempting to acquire the lock there will be a constant large amount of competition around the lock, meaning there is a ton of bus traffic.