When we look at the performance of QUIC, we often find that the limiting factor is CPU consumption of socket calls and crypto processing. It is, but congestion control also matters quite a big. In this blog (https://www.privateoctopus.com/2026/01/30/cpu_bound.html) I explain how fixing the "max RTT" measurement and the pacing algorithm for the C4 algorithm improved tests of picoquic on loopback from "worse than BBR" to "better than Cubic".