Interesting.. QUIC isn’t very quick over fast internet.

QUIC is expected to be a game-changer in improving web application performance. In this paper, we conduct a systematic examination of QUIC’s performance over high-speed networks. We find that over fast Internet, the UDP+QUIC+HTTP/3 stack suffers a data rate reduction of up to 45.2% compared to the TCP+TLS+HTTP/2 counterpart. Moreover, the performance gap between QUIC and HTTP/2 grows as the underlying bandwidth increases. We observe this issue on lightweight data transfer clients and major web browsers (Chrome, Edge, Firefox, Opera), on different hosts (desktop, mobile), and over diverse networks (wired broadband, cellular). It affects not only file transfers, but also various applications such as video streaming (up to 9.8% video bitrate reduction) and web browsing. Through rigorous packet trace analysis and kernel- and user-space profiling, we identify the root cause to be high receiver-side processing overhead, in particular, excessive data packets and QUIC’s user-space ACKs. We make concrete recommendations for mitigating the observed performance issues.

https://dl.acm.org/doi/10.1145/3589334.3645323

@xuu Thanks for the link. I found a pdf on one of the authors’ home pages: https://ahmadhassandebugs.github.io/assets/pdf/quic_www24.pdf . I wonder how the protocol was evaluated closer to the time it became a standard, and whether anything has changed. I wonder if network speeds have grown faster than CPU speeds since then. The paper says the performance is around the same below around 600 Mbps.

To be fair, I don’t think QUIC was ever expected to be faster for transferring a single stream of data. I think QUIC is supposed to reduce the impact of a dropped packet by making sure it only affects the stream it’s part of. I imagine QUIC still has that advantage, and this paper is showing the other side of a tradeoff.

What were the recommended mitigations?

@prologic@twtxt.net

They’re in Section 6:

• Receiver should adopt UDP GRO. (Something about saving CPU processing UDP packets; I’m a but fuzzy about it.) And they have suggestions for making GRO more useful for QUIC.

• Some other receiver-side suggestions: “sending delayed QUICK ACKs”; “using recvmsg to read multiple UDF packets in a single system call”.

• Use multiple threads when receiving large files.