Hi Stefano, On Mon, 2025-12-08 at 09:25 +0100, Stefano Brivio wrote:
but, in general, I don't think things can work reliably with the values you shared for tcp_notsent_lowat.
Ok, that works for me. I know very little about TCP, so I just blindly copied that value for tcp_notsent_lowat from https://blog.cloudflare.com/http-2-prioritization-with-nginx/ but if that's incompatible with pasta, then I have no problem resetting tcp_notsent_lowat back to the kernel default. A random web search makes it look like changing tcp_notsent_lowat is somewhat common https://www.google.com/search?q=tcp_notsent_lowat%3D131072 https://github.com/search?q=tcp_notsent_lowat%3D131072+NOT+is%3Afork&type=code so maybe it would be a good idea for pasta to either use setsockopt to override it, or to print a warning on startup if the sysctl is set too low?
Does this (upload now taking longer/timing out with 50 ms RTT) also happen without "custom" values for tcp_notsent_lowat?
I tested things quite extensively in that RTT region (without custom sysctl values) and the improvement looks rather consistent to me.
Ok, with tcp_notsent_lowat reset to the Fedora defaults, the upload speeds with large RTTs do indeed look *much* better $ sudo dnf install <freshly built pasta rpms> $ pasta --version pasta 0^20251208.g5943ea4-1.fc43.x86_64 $ ./pasta-upload-test.sh network ping_time wmem_max rmem_max tcp_notsent_lowat tcp_congestion_control default_qdisc download_time upload_time host 50ms custom custom default custom custom 1.561761 2.045501 pasta 50ms custom custom default custom custom 1.575290 1.707500 host 170ms custom custom default custom custom 9.147689 3.220591 pasta 170ms custom custom default custom custom 13.351799 3.411078 $ sudo dnf downgrade pasta $ pasta --version # Back to the stock pasta in F43 pasta 0^20250919.g623dbf6-1.fc43.x86_64 $ ./pasta-upload-test.sh network ping_time wmem_max rmem_max tcp_notsent_lowat tcp_congestion_control default_qdisc download_time upload_time host 50ms custom custom default custom custom 1.429540 1.674165 pasta 50ms custom custom default custom custom 1.503907 2.025471 host 170ms custom custom default custom custom 8.891267 3.039416 pasta 170ms custom custom default custom custom 11.056843 18.704653 Thanks again for all your help, -- Max