[tor-bugs] #24973 [Core Tor/Tor]: Tor should be more gentle when launching dozens of circuits at once

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#24973: Tor should be more gentle when launching dozens of circuits at once
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     Reporter:  asn           |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: unspecified
     Severity:  Normal        |   Keywords:  tor-dos tor-hs performance
Actual Points:                |  Parent ID:
       Points:  3             |   Reviewer:
      Sponsor:                |
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 When starting up Tor as an HS, Tor will create dozens of circs in quick
 succession (preemptive circs, HSDir circs, intro point circs, CBT circs).

 Consider a Tor that starts up with 10 HSes configured(many of those Tors
 exist); it will easily attempt to make hundreds of circuits within
 seconds.

 It might make sense to have some sort of circuit rate limiting during
 startup to avoid flooding our guard with so many circuit creations. I
 notice that Tor will whine about the guard failing circuits during startup
 very often, and perhaps this initial circuit flood is what's causing it?

 We already have `MaxClientCircuitsPending` but not sure if that's enough.
 We also used to delay bootup of multiple onion services, but not sure we
 do this anymore (can't see it in `hs_config_service_all()`).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24973>
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