[tor-bugs] #29494 [Core Tor/Tor]: Optimize interaction between circuitmux and circuitpadding

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#29494: Optimize interaction between circuitmux and circuitpadding
------------------------------+-----------------------
     Reporter:  mikeperry     |      Owner:  mikeperry
         Type:  enhancement   |     Status:  assigned
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  wtf-pad
Actual Points:                |  Parent ID:
       Points:  5             |   Reviewer:
      Sponsor:  Sponsor2      |
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 In #29204, we realized that we needed to inspect the circuit queue to
 prevent the circuit padding system from queuing too much padding. For that
 ticket, we're going to do the simple fix -- we don't schedule padding if
 the circuit's cell queue already has a window full of cells on it. In that
 case, we just lie to circpad and tell the machine we sent padding even
 though we did not.

 However, we should determine if we want to have a more complicated
 interaction, such as delaying our padding until the queue drains. We
 should also examine creating alternate machine events for when cells are
 dequeued from circuitmux vs when they are sent locally. This has pluses
 and minuses for machine interaction.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29494>
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