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GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.

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  • #33763

Closed (moved)
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Opened Mar 30, 2020 by David Goulet@dgoulet🐋

Consider setting TCP_NOTSENT_LOWAT to 1 byte on our TCP connections

This TCP option would provide us and important performance benefit at the relay side.

In an effort to work on a new tor design to reduce kernel queuing delays, see it as an improvement to KIST and tor architecture, Rob and I submitted this paper to NetDev 0x14 conference in hope of sitting down with the Linux kernel developers and network experts about this idea.

https://www.robgjansen.com/publications/epollcwnd-netdev2020.pdf

Ultimately we want a new poll TCP option in the kernel which our experimentation shows how it improves performance drastically.

But turns out that starting with setting TCP_NOTSENT_LOWAT to 1 byte would significantly improve performance close to what we wanted. See Figure 1. (page 3) in the paper for the performance improvements.

Setting TCP_NOTSENT_LOWAT is minimal change to tor and thus we should do it.

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Reference: legacy/trac#33763