[tor-bugs] #7291 [Tor]: Investigate making MaxOnionsPending time-based

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#7291: Investigate making MaxOnionsPending time-based
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 Reporter:  mikeperry    |          Owner:                    
     Type:  enhancement  |         Status:  needs_review      
 Priority:  normal       |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor          |        Version:                    
 Keywords:  tor-relay    |         Parent:                    
   Points:               |   Actualpoints:                    
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Changes (by nickm):

  * status:  new => needs_review


Comment:

 I've done a branch "onionqueue_timer" to keep track of how long onions
 have been in the queue for before they get handed off to a cpuworker.  If
 as I suspect the answer is something like (150 msec / NumCPUs), then we
 should consider a new approach.

 A more reasonable approach is something like: Let T_max be the longest
 amount of time we're willing to queue an onionskin for.  Let T_o be the
 time it takes to process an onionskin.  Don't queue more than NumCPUs *
 (T_max / T_o) onionskins.  Assuming a modest server like my laptop,
 setting T_max == 1 sec, NumCPUs == 4, and T_o == 2.2 msec, that gives
 something more like 1800 as a good limit for a modest server.

 Having both ntor and TAP onionskins will complicate this a little, but not
 by too much.

 If we start to recommend high values for MaxOnionsPending, we should look
 closely at the code for onion_pending_remove: It does a linear search over
 the queue, which is probably not so good if we're looking forward to a
 time of super-fast servers with leneant timeouts and a large volume of
 ntor traffic. (T_max = 2 s, NumCPUS == 16, T_o == 150 usec => Wow, would
 we even ever want to allow that?)

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7291#comment:4>
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