Hello,

I have been experimenting with the new HTTP/3 quic feature in nginx,

I have noticed that as latency increases, the throughput of download speed seems to exponentially decrease. H2 traffic over TCP does not have the same effect.

At a ping of around 270ms, I see nginx's quic implementation crawl to a download speed of 200KB per second.

Here is my example: Two servers in data centers, both with 10 gigabit internet connections. One in Australia, the other in the UK. iperf3 tests over UDP yields 700mbits per second between them both ways.

H2 over TCP = 42 MBytes per second. Downloads 1G in 27 seconds.
# curl https://www.afamsterdam.nl/1GB.iso > /dev/null
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1024M 100 1024M 0 0 36.8M 0 0:00:27 0:00:27 --:--:-- 42.5M

H3 over UDP = 240KB per second. Did not wait for test to finish (1.5 hours remaining).
# curl --http3 https://www.afamsterdam.nl/1GB.iso > /dev/null
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 1024M 0 7460k 0 0 226k 0 1:16:59 0:00:32 1:16:27 244k^C

When I run a http3 test from a low latency, the speed is similar, though still a bit slower than TCP.

This slowness presents itself in chrome too (1MB images take 9 seconds to download over 1 second on H2). Nothing was seemingly unusual in a chrome export quic JSON dump.

Any ideas?

nginx version: nginx/1.25.2
built by gcc 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04)
built with OpenSSL 3.0.10+quic 1 Aug 2023
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp --http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp --http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx --with-compat --with-file-aio --with-threads --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_flv_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_mp4_module --with-http_random_index_module --with-http_realip_module --with-http_secure_link_module --with-http_slice_module --with-http_ssl_module --with-http_stub_status_module --with-http_sub_module --with-http_v2_module --with-http_v3_module --with-http_ssl_module --with-stream --with-stream_realip_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-compat --add-dynamic-module=../ngx_brotli --add-module=/tmp/modsecurity_nginx/modsecurity-nginx-v1.0.3 --with-openssl=../openssl-openssl-3.0.10-quic1 --with-cc-opt='-g -O2 -ffile-prefix-map=/data/builder/debuild/nginx-1.25.2/debian/debuild-base/nginx-1.25.2=. -flto=auto -ffat-lto-objects -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fPIC' --with-ld-opt='-Wl,-Bsymbolic-functions -flto=auto -ffat-lto-objects -flto=auto -Wl,-z,relro -Wl,-z,now -Wl,--as-needed -pie'