Isn't event loop going to take up lot of CPU time as it is basically a while loop?

[activeLearner]

From this official Qt documentation event loop conceptually executes as follows:

while (is_active) {
while (!event_queue_is_empty)
dispatch_next_event();
wait_for_more_events(); 
}

while (is_active) {
while (!event_queue_is_empty)
dispatch_next_event();
wait_for_more_events(); 
}

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As one can observe that Qt application will utilise the CPU all the time as it needs to keep running the loop for its GUI to be updated. If this is the case what happens when multiple threads run concurrently in addition to GUI thread? Will the performance degrade while multi tasking?