[tor-bugs] #21421 [Core Tor/Tor]: Maybe check for GUARD_WAIT circuit readiness whenever a guard fails

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#21421: Maybe check for GUARD_WAIT circuit readiness whenever a guard fails
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     Reporter:  nickm         |      Owner:
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: unspecified
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  guards performance
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 Right now we check whether any `GUARD_WAIT` circuits can become usable
 (`OPEN`) once a second or so, in
 `circuit_upgrade_circuits_from_guard_wait()`.  But maybe we should do so
 more often -- possibly, whenever a guard is marked as down?

 This would make some streams attach up to one second faster -- but only in
 the cases when primary guards are down but we expected them to be up.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21421>
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