“Light can travel roughly 30 cm in one nanosecond so you may be wondering why this signal is traveling so slow.”
Two Xbox 360 cores sat 5.5 mm farther from the L2 cache and paid four extra cycles for it. You can see the delay on the die shot. Dawson corrected his own headline the next day, since the signal actually covers 11 mm round trip. Physics sets the latency, and no compiler flag gets it back.