Read on to learn how we used network packet captures and BPF to debug web server performance, ultimately uncovering a Linux kernel performance issue. This investigation was a collaboration between myself and my colleagues. Contents Background What are listen overflows? What’s causing listen overflows? Why were web requests served slowly in the first few minutes after new hosts were pooled? Is it the network? (no) Is it due to elevated system CPU? (yes) Why did we initially suspect the network? W...