From 0ae0b5aa4136fe6df7863c8a5b7d239d519b7393 Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Wed, 12 Jul 2017 12:17:51 -0400
Subject: [PATCH] Queue consensus diffs at LOW priority.

Fixes bug 22883.
---
 changes/bug22883-priority   |  8 ++++++++
 src/or/consdiffmgr.c        |  6 ++++--
 src/or/cpuworker.c          | 15 +++++++++------
 src/or/cpuworker.h          |  2 ++
 src/test/test_consdiffmgr.c |  5 ++++-
 5 files changed, 27 insertions(+), 9 deletions(-)
 create mode 100644 changes/bug22883-priority

diff --git a/changes/bug22883-priority b/changes/bug22883-priority
new file mode 100644
index 0000000000..4b3531c30b
--- /dev/null
+++ b/changes/bug22883-priority
@@ -0,0 +1,8 @@
+  o Major bugfixes (relay, performance):
+
+    - Perform circuit handshake operations at a higher priority than we use
+      for consensus diff creation and compression. This should prevent
+      circuits from starving when a relay or bridge receive a new consensus,
+      especially on lower-powered machines. Fixes bug 22883; bugfix on
+      0.3.1.1-alpha.
+
diff --git a/src/or/consdiffmgr.c b/src/or/consdiffmgr.c
index 638fcd6794..8d0a0af3d5 100644
--- a/src/or/consdiffmgr.c
+++ b/src/or/consdiffmgr.c
@@ -1605,7 +1605,8 @@ consensus_diff_queue_diff_work(consensus_cache_entry_t *diff_from,
     goto err;
 
   workqueue_entry_t *work;
-  work = cpuworker_queue_work(consensus_diff_worker_threadfn,
+  work = cpuworker_queue_work(WQ_PRI_LOW,
+                              consensus_diff_worker_threadfn,
                               consensus_diff_worker_replyfn,
                               job);
   if (!work)
@@ -1768,7 +1769,8 @@ consensus_queue_compression_work(const char *consensus,
 
   if (background_compression) {
     workqueue_entry_t *work;
-    work = cpuworker_queue_work(consensus_compress_worker_threadfn,
+    work = cpuworker_queue_work(WQ_PRI_LOW,
+                                consensus_compress_worker_threadfn,
                                 consensus_compress_worker_replyfn,
                                 job);
     if (!work) {
diff --git a/src/or/cpuworker.c b/src/or/cpuworker.c
index 1013fa555e..ad99af64c0 100644
--- a/src/or/cpuworker.c
+++ b/src/or/cpuworker.c
@@ -481,16 +481,18 @@ queue_pending_tasks(void)
 
 /** DOCDOC */
 MOCK_IMPL(workqueue_entry_t *,
-cpuworker_queue_work,(workqueue_reply_t (*fn)(void *, void *),
+cpuworker_queue_work,(workqueue_priority_t priority,
+                      workqueue_reply_t (*fn)(void *, void *),
                       void (*reply_fn)(void *),
                       void *arg))
 {
   tor_assert(threadpool);
 
-  return threadpool_queue_work(threadpool,
-                               fn,
-                               reply_fn,
-                               arg);
+  return threadpool_queue_work_priority(threadpool,
+                                        priority,
+                                        fn,
+                                        reply_fn,
+                                        arg);
 }
 
 /** Try to tell a cpuworker to perform the public key operations necessary to
@@ -545,7 +547,8 @@ assign_onionskin_to_cpuworker(or_circuit_t *circ,
   memwipe(&req, 0, sizeof(req));
 
   ++total_pending_tasks;
-  queue_entry = threadpool_queue_work(threadpool,
+  queue_entry = threadpool_queue_work_priority(threadpool,
+                                      WQ_PRI_HIGH,
                                       cpuworker_onion_handshake_threadfn,
                                       cpuworker_onion_handshake_replyfn,
                                       job);
diff --git a/src/or/cpuworker.h b/src/or/cpuworker.h
index aedf2fae32..320de9532f 100644
--- a/src/or/cpuworker.h
+++ b/src/or/cpuworker.h
@@ -16,7 +16,9 @@ void cpu_init(void);
 void cpuworkers_rotate_keyinfo(void);
 struct workqueue_entry_s;
 enum workqueue_reply_t;
+enum workqueue_priority_t;
 MOCK_DECL(struct workqueue_entry_s *, cpuworker_queue_work, (
+                    enum workqueue_priority_t priority,
                     enum workqueue_reply_t (*fn)(void *, void *),
                     void (*reply_fn)(void *),
                     void *arg));
diff --git a/src/test/test_consdiffmgr.c b/src/test/test_consdiffmgr.c
index 746d17a038..963a6e427a 100644
--- a/src/test/test_consdiffmgr.c
+++ b/src/test/test_consdiffmgr.c
@@ -98,10 +98,13 @@ typedef struct fake_work_queue_ent_t {
   void *arg;
 } fake_work_queue_ent_t;
 static struct workqueue_entry_s *
-mock_cpuworker_queue_work(enum workqueue_reply_t (*fn)(void *, void *),
+mock_cpuworker_queue_work(workqueue_priority_t prio,
+                          enum workqueue_reply_t (*fn)(void *, void *),
                           void (*reply_fn)(void *),
                           void *arg)
 {
+  (void) prio;
+
   if (! fake_cpuworker_queue)
     fake_cpuworker_queue = smartlist_new();