[tor-commits] [tor] 73/77: hs_pow: always give other events a chance to run between rend requests

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dgoulet pushed a commit to branch main
in repository tor.

commit a13d7bd5e96765ac7c660415a498d9d9100ade62
Author: Micah Elizabeth Scott <beth@xxxxxxxxxxxxxx>
AuthorDate: Tue Apr 11 10:28:09 2023 -0700

    hs_pow: always give other events a chance to run between rend requests
    
    This dequeue path has been through a few revisions by now, first
    limiting us to a fixed number per event loop callback, then an
    additional limit based on a token bucket, then the current version
    which has only the token bucket.
    
    The thinking behing processing multiple requests per callback was to
    optimize our usage of libevent, but in effect this creates a
    prioritization problem. I think even a small fixed limit would be less
    reliable than just backing out this optimization and always allowing
    other callbacks to interrupt us in-between dequeues.
    
    With this patch I'm seeing much smoother queueing behavior when I add
    artificial delays to the main thread in testing.
    
    Signed-off-by: Micah Elizabeth Scott <beth@xxxxxxxxxxxxxx>
---
 src/feature/hs/hs_circuit.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/feature/hs/hs_circuit.c b/src/feature/hs/hs_circuit.c
index c3f2fbfc1e..ccd6711041 100644
--- a/src/feature/hs/hs_circuit.c
+++ b/src/feature/hs/hs_circuit.c
@@ -767,7 +767,9 @@ handle_rend_pqueue_cb(mainloop_event_t *ev, void *arg)
            in_flight,
            smartlist_len(pow_state->rend_request_pqueue));
 
-  /* Process rendezvous request until the maximum per mainloop run. */
+  /* Process only one rend request per callback, so that this work will not
+   * be prioritized over other event loop callbacks. We may need to retry
+   * in order to find one request that's still viable. */
   while (smartlist_len(pow_state->rend_request_pqueue) > 0) {
 
     /* first, peek at the top result to see if we want to pop it */
@@ -827,11 +829,7 @@ handle_rend_pqueue_cb(mainloop_event_t *ev, void *arg)
 
     ++pow_state->rend_handled;
     ++in_flight;
-
-    if (pow_state->using_pqueue_bucket &&
-        token_bucket_ctr_get(&pow_state->pqueue_bucket) < 1) {
-      break;
-    }
+    break;
   }
 
   /* If there are still some pending rendezvous circuits in the pqueue then

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