Currently the ovs-tcpdump utility creates a virtual tunnel to send
packets to. This method functions perfectly fine, however, it can
greatly impact performance of the monitored port.
It has been reported to reduce packet throughput significantly. I was
able to reproduce a reduction in throughput of up 70 percent in some
tests with a simple setup of two hosts communicating through a single
bridge on Linux with the kernel module datapath. Another more complex
test was configured for DPDK and the usermode datapath. This test
involved a data path going from a VM, through a port into one OVS
bridge, out through a network card which could be DPDK enabled for the
relevant tests, in to a different network interface, then into a
different OVS bridge, through another port, and then into a virtual
machine.
Using the dummy driver resulted in the following impact to performance
compared to no ovs-tcpdump. Due to intra-test variance and fluctuations
during the first few seconds after installing a tap; multiple samples
were taken over multiple test runs. The first few seconds worth of
results were discarded and then results were averaged out.
Original Script
===============
Category Impact on Throughput
Kernel datapath - 65%
Usermode datapath - 26%
DPDK datapath - 37%
New Script
==========
Category Impact on Throughput
Kernel datapath - 5%
Usermode datapath - 16%
DPDK datapath - 29%
Signed-off-by: Mike Pattrick <m...@redhat.com>
---
utilities/ovs-tcpdump.in | 42 +++++++++++++++++++++-------------------
1 file changed, 22 insertions(+), 20 deletions(-)
diff --git a/utilities/ovs-tcpdump.in b/utilities/ovs-tcpdump.in
index 5ec02383c..10989dfc1 100755
--- a/utilities/ovs-tcpdump.in
+++ b/utilities/ovs-tcpdump.in
@@ -14,12 +14,9 @@
# See the License for the specific language governing permissions and
# limitations under the License.
-import fcntl
-
import os
import pwd
from random import randint
-import struct
import subprocess
import sys
import time
@@ -52,8 +49,8 @@ except Exception:
print(" the correct location.")
sys.exit(1)
-tapdev_fd = None
_make_taps = {}
+_del_taps = {}
_make_mirror_name = {}
IFNAMSIZ_LINUX = 15 # this is the max name size, excluding the null byte.
@@ -67,21 +64,11 @@ def _doexec(*args, **kwargs):
return proc
-def _install_tap_linux(tap_name, mtu_value=None):
- """Uses /dev/net/tun to create a tap device"""
- global tapdev_fd
-
- IFF_TAP = 0x0002
- IFF_NO_PI = 0x1000
- TUNSETIFF = 0x400454CA # This is derived by printf() of TUNSETIFF
- TUNSETOWNER = TUNSETIFF + 2
-
- tapdev_fd = os.open('/dev/net/tun', os.O_RDWR)
- ifr = struct.pack('16sH', tap_name.encode('utf8'), IFF_TAP | IFF_NO_PI)
- fcntl.ioctl(tapdev_fd, TUNSETIFF, ifr)
- fcntl.ioctl(tapdev_fd, TUNSETOWNER, os.getegid())
+def _install_dst_if_linux(tap_name, mtu_value=None):
+ _doexec(
+ *['ip', 'link', 'add', str(tap_name), 'type', 'dummy']
+ ).wait()
- time.sleep(1) # required to give the new device settling time
if mtu_value is not None:
pipe = _doexec(
*(['ip', 'link', 'set', 'dev', str(tap_name), 'mtu',
@@ -93,14 +80,22 @@ def _install_tap_linux(tap_name, mtu_value=None):
pipe.wait()
+def _remove_dst_if_linux(tap_name):
+ _doexec(
+ *['ip', 'link', 'del', str(tap_name)]
+ ).wait()
+
+
def _make_linux_mirror_name(interface_name):
if len(interface_name) > IFNAMSIZ_LINUX - 2:
return "ovsmi%06d" % randint(1, 999999)
return "mi%s" % interface_name
-_make_taps['linux'] = _install_tap_linux
-_make_taps['linux2'] = _install_tap_linux
+_make_taps['linux'] = _install_dst_if_linux
+_make_taps['linux2'] = _install_dst_if_linux
+_del_taps['linux'] = _remove_dst_if_linux
+_del_taps['linux2'] = _remove_dst_if_linux
_make_mirror_name['linux'] = _make_linux_mirror_name
_make_mirror_name['linux2'] = _make_linux_mirror_name
@@ -455,6 +450,9 @@ def main():
mirror_interface not in interfaces():
_make_taps[sys.platform](mirror_interface,
ovsdb.interface_mtu(interface))
+ tap_created = True
+ else:
+ tap_created = False
if mirror_interface not in interfaces():
print("ERROR: Please create an interface called `%s`" %
@@ -480,6 +478,8 @@ def main():
print("ERROR: Unable to properly setup the mirror: %s." % str(oe))
try:
ovsdb.destroy_port(mirror_interface, ovsdb.port_bridge(interface))
+ if tap_created is True:
+ _del_taps[sys.platform](mirror_interface)
except Exception:
pass
sys.exit(1)
@@ -498,6 +498,8 @@ def main():
ovsdb.destroy_mirror(interface, ovsdb.port_bridge(interface))
ovsdb.destroy_port(mirror_interface, ovsdb.port_bridge(interface))
+ if tap_created is True:
+ _del_taps[sys.platform](mirror_interface)
except Exception:
print("Unable to tear down the ports and mirrors.")
print("Please use ovs-vsctl to remove the ports and mirrors created.")
--
2.30.2
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