diff --git a/synapse/util/logcontext.py b/synapse/util/logcontext.py

index eab9d57650..a58c723403 100644
--- a/synapse/util/logcontext.py
+++ b/synapse/util/logcontext.py
@@ -59,8 +59,8 @@ class LoggingContext(object):
 
     __slots__ = [
         "previous_context", "name", "ru_stime", "ru_utime",
-        "db_txn_count", "db_txn_duration_ms", "db_sched_duration_ms",
-        "usage_start", "usage_end",
+        "db_txn_count", "db_txn_duration_sec", "db_sched_duration_sec",
+        "usage_start",
         "main_thread", "alive",
         "request", "tag",
     ]
@@ -84,10 +84,10 @@ class LoggingContext(object):
         def stop(self):
             pass
 
-        def add_database_transaction(self, duration_ms):
+        def add_database_transaction(self, duration_sec):
             pass
 
-        def add_database_scheduled(self, sched_ms):
+        def add_database_scheduled(self, sched_sec):
             pass
 
         def __nonzero__(self):
@@ -103,14 +103,16 @@ class LoggingContext(object):
         self.ru_utime = 0.
         self.db_txn_count = 0
 
-        # ms spent waiting for db txns, excluding scheduling time
-        self.db_txn_duration_ms = 0
+        # sec spent waiting for db txns, excluding scheduling time
+        self.db_txn_duration_sec = 0
 
-        # ms spent waiting for db txns to be scheduled
-        self.db_sched_duration_ms = 0
+        # sec spent waiting for db txns to be scheduled
+        self.db_sched_duration_sec = 0
 
+        # If alive has the thread resource usage when the logcontext last
+        # became active.
         self.usage_start = None
-        self.usage_end = None
+
         self.main_thread = threading.current_thread()
         self.request = None
         self.tag = ""
@@ -159,7 +161,7 @@ class LoggingContext(object):
         """Restore the logging context in thread local storage to the state it
         was before this context was entered.
         Returns:
-            None to avoid suppressing any exeptions that were thrown.
+            None to avoid suppressing any exceptions that were thrown.
         """
         current = self.set_current_context(self.previous_context)
         if current is not self:
@@ -185,47 +187,61 @@ class LoggingContext(object):
 
     def start(self):
         if threading.current_thread() is not self.main_thread:
+            logger.warning("Started logcontext %s on different thread", self)
             return
 
-        if self.usage_start and self.usage_end:
-            self.ru_utime += self.usage_end.ru_utime - self.usage_start.ru_utime
-            self.ru_stime += self.usage_end.ru_stime - self.usage_start.ru_stime
-            self.usage_start = None
-            self.usage_end = None
-
+        # If we haven't already started record the thread resource usage so
+        # far
         if not self.usage_start:
             self.usage_start = get_thread_resource_usage()
 
     def stop(self):
         if threading.current_thread() is not self.main_thread:
+            logger.warning("Stopped logcontext %s on different thread", self)
             return
 
+        # When we stop, let's record the resource used since we started
         if self.usage_start:
-            self.usage_end = get_thread_resource_usage()
+            usage_end = get_thread_resource_usage()
+
+            self.ru_utime += usage_end.ru_utime - self.usage_start.ru_utime
+            self.ru_stime += usage_end.ru_stime - self.usage_start.ru_stime
+
+            self.usage_start = None
+        else:
+            logger.warning("Called stop on logcontext %s without calling start", self)
 
     def get_resource_usage(self):
+        """Get CPU time used by this logcontext so far.
+
+        Returns:
+            tuple[float, float]: The user and system CPU usage in seconds
+        """
         ru_utime = self.ru_utime
         ru_stime = self.ru_stime
 
-        if self.usage_start and threading.current_thread() is self.main_thread:
+        # If we are on the correct thread and we're currently running then we
+        # can include resource usage so far.
+        is_main_thread = threading.current_thread() is self.main_thread
+        if self.alive and self.usage_start and is_main_thread:
             current = get_thread_resource_usage()
             ru_utime += current.ru_utime - self.usage_start.ru_utime
             ru_stime += current.ru_stime - self.usage_start.ru_stime
 
         return ru_utime, ru_stime
 
-    def add_database_transaction(self, duration_ms):
+    def add_database_transaction(self, duration_sec):
         self.db_txn_count += 1
-        self.db_txn_duration_ms += duration_ms
+        self.db_txn_duration_sec += duration_sec
 
-    def add_database_scheduled(self, sched_ms):
+    def add_database_scheduled(self, sched_sec):
         """Record a use of the database pool
 
         Args:
-            sched_ms (int): number of milliseconds it took us to get a
+            sched_sec (float): number of seconds it took us to get a
                 connection
         """
-        self.db_sched_duration_ms += sched_ms
+        self.db_sched_duration_sec += sched_sec
 
 
 class LoggingContextFilter(logging.Filter):