[tor-bugs] #33763 [Core Tor/Tor]: Consider setting TCP_NOTSENT_LOWAT to 1 byte on our TCP connections

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#33763: Consider setting TCP_NOTSENT_LOWAT to 1 byte on our TCP connections
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     Reporter:  dgoulet    |      Owner:  (none)
         Type:             |     Status:  new
  enhancement              |
     Priority:  Medium     |  Milestone:  Tor: 0.4.4.x-final
    Component:  Core       |    Version:
  Tor/Tor                  |
     Severity:  Normal     |   Keywords:  tor-relay performance scaling tcp
Actual Points:             |  Parent ID:
       Points:  0.2        |   Reviewer:
      Sponsor:             |
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 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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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33763>
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