diff --git a/oft b/oft
index 4ef82eb..9d5df6a 100755
--- a/oft
+++ b/oft
@@ -77,12 +77,14 @@
     "log_file"           : "oft.log",
     "log_dir"            : None,
     "debug"              : "verbose",
+    "profile"            : False,
 
     # Test behavior options
     "relax"              : False,
     "test_params"        : "None",
     "fail_skipped"       : False,
-    "default_timeout"    : 2,
+    "default_timeout"    : 2.0,
+    "default_negative_timeout" : 0.01,
     "minsize"            : 0,
     "random_seed"        : None,
     "disable_ipv6"       : False,
@@ -179,6 +181,7 @@
                      const="verbose", help="Shortcut for --debug=verbose")
     group.add_option("-q", "--quiet", action="store_const", dest="debug",
                      const="warning", help="Shortcut for --debug=warning")
+    group.add_option("--profile", action="store_true", help="Write Python profile to profile.out")
     parser.add_option_group(group)
 
     group = optparse.OptionGroup(parser, "Test behavior options")
@@ -189,8 +192,10 @@
     group.add_option("-t", "--test-params", help=test_params_help)
     group.add_option("--fail-skipped", action="store_true",
                       help="Return failure if any test was skipped")
-    group.add_option("--default-timeout", type="int",
+    group.add_option("--default-timeout", type=float,
                       help="Timeout in seconds for most operations")
+    group.add_option("--default-negative-timeout", type=float,
+                      help="Timeout in seconds for negative checks")
     group.add_option("--minsize", type="int",
                       help="Minimum allowable packet size on the dataplane.")
     group.add_option("--random-seed", type="int",
@@ -491,6 +496,7 @@
 logging.info("OF port map: " + str(config["port_map"]))
 
 oftest.ofutils.default_timeout = config["default_timeout"]
+oftest.ofutils.default_negative_timeout = config["default_negative_timeout"]
 oftest.testutils.MINSIZE = config['minsize']
 
 if os.getuid() != 0 and not config["allow_user"]:
@@ -512,6 +518,11 @@
 signal.signal(signal.SIGINT, signal.SIG_DFL)
 
 if __name__ == "__main__":
+    if config["profile"]:
+        import cProfile
+        profiler = cProfile.Profile()
+        profiler.enable()
+
     # Set up the dataplane
     oftest.dataplane_instance = oftest.dataplane.DataPlane(config)
     pcap_setup(config)
@@ -532,6 +543,10 @@
     oftest.dataplane_instance.kill()
     oftest.dataplane_instance = None
 
+    if config["profile"]:
+        profiler.disable()
+        profiler.dump_stats("profile.out")
+
     if result.failures or result.errors:
         # exit(1) hangs sometimes
         os._exit(1)
diff --git a/src/python/oftest/ofutils.py b/src/python/oftest/ofutils.py
index 8cf2ae0..f81a2f5 100644
--- a/src/python/oftest/ofutils.py
+++ b/src/python/oftest/ofutils.py
@@ -10,6 +10,7 @@
 import logging
 
 default_timeout = None # set by oft
+default_negative_timeout = None # set by oft
 
 def gen_xid():
     return random.randrange(1,0xffffffff)
@@ -19,11 +20,9 @@
 The condition variable must already be acquired.
 The timeout value -1 means use the default timeout.
 There is deliberately no support for an infinite timeout.
-TODO: get the default timeout from configuration
 """
 def timed_wait(cv, fn, timeout=-1):
     if timeout == -1:
-        # TODO make this configurable
         timeout = default_timeout
 
     end_time = time.time() + timeout
diff --git a/src/python/oftest/testutils.py b/src/python/oftest/testutils.py
index 5b2e365..104d3b5 100644
--- a/src/python/oftest/testutils.py
+++ b/src/python/oftest/testutils.py
@@ -576,11 +576,6 @@
     DEPRECATED in favor in verify_packets
     """
 
-    # Wait this long for packets that we don't expect to receive.
-    # 100ms is (rarely) too short for positive tests on slow
-    # switches but is definitely not too short for a negative test.
-    negative_timeout = 0.1
-
     exp_pkt_arg = None
     if oftest.config["relax"]:
         exp_pkt_arg = pkt
@@ -598,7 +593,7 @@
                              "Received packet does not match expected packet " +
                              "on port " + str(ofport))
     if len(no_ports) > 0:
-        time.sleep(negative_timeout)
+        time.sleep(oftest.ofutils.default_negative_timeout)
     for ofport in no_ports:
         logging.debug("Negative check for pkt on port " + str(ofport))
         (rcv_port, rcv_pkt, pkt_time) = dp.poll(
@@ -1605,7 +1600,7 @@
 
     # Negative test, need to wait a short amount of time before checking we
     # didn't receive the message.
-    time.sleep(0.5)
+    time.sleep(oftest.ofutils.default_negative_timeout)
 
     # Check every packet_in queued in the controller
     while True:
@@ -1648,7 +1643,10 @@
     Check that a particular packet is not received
     """
     logging.debug("Negative check for pkt on port %r", ofport)
-    (rcv_port, rcv_pkt, pkt_time) = test.dataplane.poll(port_number=ofport, exp_pkt=str(pkt), timeout=0.01)
+    (rcv_port, rcv_pkt, pkt_time) = \
+        test.dataplane.poll(
+            port_number=ofport, exp_pkt=str(pkt),
+            timeout=oftest.ofutils.default_negative_timeout)
     test.assertTrue(rcv_pkt == None, "Received packet on %r" % ofport)
 
 def verify_no_other_packets(test):
@@ -1660,7 +1658,7 @@
     if oftest.config["relax"]:
         return
     logging.debug("Checking for unexpected packets on all ports")
-    (rcv_port, rcv_pkt, pkt_time) = test.dataplane.poll(timeout=0.01)
+    (rcv_port, rcv_pkt, pkt_time) = test.dataplane.poll(timeout=oftest.ofutils.default_negative_timeout)
     if rcv_pkt != None:
         logging.debug("Received unexpected packet on port %r: %s", rcv_port, format_packet(rcv_pkt))
     test.assertTrue(rcv_pkt == None, "Unexpected packet on port %r" % rcv_port)
diff --git a/tests/latency.py b/tests/latency.py
new file mode 100644
index 0000000..3cf8c5d
--- /dev/null
+++ b/tests/latency.py
@@ -0,0 +1,107 @@
+"""
+Latency tests
+
+These tests are mostly helpful for finding an optimal value for the
+--default-negative-timeout option. If this value is too large it will
+unnecessarily some down testing, but if it is too small then tests
+may pass when they should have failed.
+
+Most of this latency is caused by OFTest. Actual switch latency should be just
+a few microseconds, but OFTest can add milliseconds on top of that.
+"""
+
+import logging
+import unittest
+import time
+
+from oftest import config
+import ofp
+import oftest.base_tests as base_tests
+
+from oftest.testutils import *
+
+class DataplaneLatency(base_tests.SimpleDataPlane):
+    """
+    Measure and assert dataplane latency
+
+    All packets must arrive within the default timeout, and 90% must
+    arrive within the default negative timeout.
+    """
+    def runTest(self):
+        in_port, out_port = openflow_ports(2)
+
+        delete_all_flows(self.controller)
+
+        pkt = str(simple_tcp_packet())
+
+        request = ofp.message.flow_add(
+            match=ofp.match(wildcards=ofp.OFPFW_ALL),
+            buffer_id=0xffffffff,
+            actions=[ofp.action.output(out_port)])
+        
+        self.controller.message_send(request)
+        do_barrier(self.controller)
+
+        latencies = []
+        for i in xrange(0, 1000):
+            start_time = time.time()
+            self.dataplane.send(in_port, pkt)
+            verify_packet(self, pkt, out_port)
+            end_time = time.time()
+            latencies.append(end_time - start_time)
+
+        latencies.sort()
+        
+        latency_min = latencies[0]
+        latency_90 = latencies[int(len(latencies)*0.9)]
+        latency_max = latencies[-1]
+
+        logging.debug("Minimum latency: %f ms", latency_min * 1000.0)
+        logging.debug("90%% latency: %f ms", latency_90 * 1000.0)
+        logging.debug("Maximum latency: %f ms", latency_max * 1000.0)
+
+        self.assertGreater(config["default_timeout"], latency_max)
+        self.assertGreater(config["default_negative_timeout"], latency_90)
+
+class PktinLatency(base_tests.SimpleDataPlane):
+    """
+    Measure and assert packet-in latency
+
+    All packet-ins must arrive within the default timeout, and 90% must
+    arrive within the default negative timeout.
+    """
+    def runTest(self):
+        in_port, = openflow_ports(1)
+
+        delete_all_flows(self.controller)
+
+        pkt = str(simple_tcp_packet())
+
+        request = ofp.message.flow_add(
+            match=ofp.match(wildcards=ofp.OFPFW_ALL),
+            buffer_id=0xffffffff,
+            actions=[ofp.action.output(ofp.OFPP_CONTROLLER)])
+        
+        self.controller.message_send(request)
+        do_barrier(self.controller)
+
+        latencies = []
+        for i in xrange(0, 1000):
+            start_time = time.time()
+            self.dataplane.send(in_port, pkt)
+            verify_packet_in(self, pkt, in_port, ofp.OFPR_ACTION)
+            end_time = time.time()
+            latencies.append(end_time - start_time)
+
+        latencies.sort()
+        
+        latency_min = latencies[0]
+        latency_90 = latencies[int(len(latencies)*0.9)]
+        latency_max = latencies[-1]
+
+        logging.debug("Minimum latency: %f ms", latency_min * 1000.0)
+        logging.debug("90%% latency: %f ms", latency_90 * 1000.0)
+        logging.debug("Maximum latency: %f ms", latency_max * 1000.0)
+
+        self.assertGreater(config["default_timeout"], latency_max)
+        self.assertGreater(config["default_negative_timeout"], latency_90)