[ovs-build] Passed: ovsrobot/ovs#2355 (series_163736 - ab45182)

Travis CI builds at travis-ci.org
Wed Mar 11 15:54:00 UTC 2020


Build Update for ovsrobot/ovs
-------------------------------------

Build: #2355
Status: Passed

Duration: 52 mins and 52 secs
Commit: ab45182 (series_163736)
Author: Vishal Deep Ajmera
Message: Avoid dp_hash recirculation for balance-tcp bond selection mode

Problem:
--------
In OVS-DPDK, flows with output over a bond interface of type “balance-tcp”
(using a hash on TCP/UDP 5-tuple) get translated by the ofproto layer into
"HASH" and "RECIRC" datapath actions. After recirculation, the packet is
forwarded to the bond member port based on 8-bits of the datapath hash
value computed through dp_hash. This causes performance degradation in the
following ways:

1. The recirculation of the packet implies another lookup of the packet’s
flow key in the exact match cache (EMC) and potentially Megaflow classifier
(DPCLS). This is the biggest cost factor.

2. The recirculated packets have a new “RSS” hash and compete with the
original packets for the scarce number of EMC slots. This implies more
EMC misses and potentially EMC thrashing causing costly DPCLS lookups.

3. The 256 extra megaflow entries per bond for dp_hash bond selection put
additional load on the revalidation threads.

Owing to this performance degradation, deployments stick to “balance-slb”
bond mode even though it does not do active-active load balancing for
VXLAN- and GRE-tunnelled traffic because all tunnel packet have the same
source MAC address.

Proposed optimization:
----------------------
This proposal introduces a new load-balancing output action instead of
recirculation.

Maintain one table per-bond (could just be an array of uint16's) and
program it the same way internal flows are created today for each possible
hash value(256 entries) from ofproto layer. Use this table to load-balance
flows as part of output action processing.

Currently xlate_normal() -> output_normal() -> bond_update_post_recirc_rules()
-> bond_may_recirc() and compose_output_action__() generate
“dp_hash(hash_l4(0))” and “recirc(<RecircID>)” actions. In this case the
RecircID identifies the bond. For the recirculated packets the ofproto layer
installs megaflow entries that match on RecircID and masked dp_hash and send
them to the corresponding output port.

Instead, we will now generate action as
    "lb_output(bond,<bond id>)"

This combines hash computation (only if needed, else re-use RSS hash) and
inline load-balancing over the bond. This action is used *only* for balance-tcp
bonds in OVS-DPDK datapath (the OVS kernel datapath remains unchanged).

Example:
--------
Current scheme:
---------------
With 1 IP-UDP flow:

flow-dump from pmd on cpu core: 2
recirc_id(0),in_port(7),packet_type(ns=0,id=0),eth(src=02:00:00:02:14:01,dst=0c:c4:7a:58:f0:2b),eth_type(0x0800),ipv4(frag=no), packets:2828969, bytes:181054016, used:0.000s, actions:hash(hash_l4(0)),recirc(0x1)

recirc_id(0x1),dp_hash(0x113683bd/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:2828937, bytes:181051968, used:0.000s, actions:2

With 8 IP-UDP flows (with random UDP src port): (all hitting same DPCL):

flow-dump from pmd on cpu core: 2
recirc_id(0),in_port(7),packet_type(ns=0,id=0),eth(src=02:00:00:02:14:01,dst=0c:c4:7a:58:f0:2b),eth_type(0x0800),ipv4(frag=no), packets:2674009, bytes:171136576, used:0.000s, actions:hash(hash_l4(0)),recirc(0x1)

recirc_id(0x1),dp_hash(0xf8e02b7e/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:377395, bytes:24153280, used:0.000s, actions:2
recirc_id(0x1),dp_hash(0xb236c260/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:333486, bytes:21343104, used:0.000s, actions:1
recirc_id(0x1),dp_hash(0x7d89eb18/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:348461, bytes:22301504, used:0.000s, actions:1
recirc_id(0x1),dp_hash(0xa78d75df/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:633353, bytes:40534592, used:0.000s, actions:2
recirc_id(0x1),dp_hash(0xb58d846f/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:319901, bytes:20473664, used:0.001s, actions:2
recirc_id(0x1),dp_hash(0x24534406/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:334985, bytes:21439040, used:0.001s, actions:1
recirc_id(0x1),dp_hash(0x3cf32550/0xff),in_port(7),packet_type(ns=0,id=0),eth_type(0x0800),ipv4(frag=no), packets:326404, bytes:20889856, used:0.001s, actions:1

New scheme:
-----------
We can do with a single flow entry (for any number of new flows):

in_port(7),packet_type(ns=0,id=0),eth(src=02:00:00:02:14:01,dst=0c:c4:7a:58:f0:2b),eth_type(0x0800),ipv4(frag=no), packets:2674009, bytes:171136576, used:0.000s, actions:lb_output(bond,1)

A new CLI has been added to dump datapath bond cache as given below.

“sudo ovs-appctl dpif-netdev/dp-bond-show [dp]”

root at ubuntu-190:performance_scripts # sudo ovs-appctl dpif-netdev/dp-bond-show
Bond cache:
        bond-id 1 :
                bucket 0 - slave 2
                bucket 1 - slave 1
                bucket 2 - slave 2
                bucket 3 - slave 1

Performance improvement:
------------------------
With a prototype of the proposed idea, the following perf improvement is seen
with Phy-VM-Phy UDP traffic, single flow. With multiple flows, the improvement
is even more enhanced (due to reduced number of flows).

1 VM:
*****
+--------------------------------------+
|                 mpps                 |
+--------------------------------------+
| Flows  master  with-opt.   %delta    |
+--------------------------------------+
| 1      4.34    5.59        28.86
| 10     4.09    5.43        32.61
| 400    3.44    5.35        55.25
| 1k     3.31    5.25        58.41
| 10k    2.46    4.43        79.78
| 100k   2.32    4.27        83.59
| 500k   2.29    4.23        84.57
+--------------------------------------+
mpps: million packets per second.
packet size 64 bytes.

Signed-off-by: Manohar Krishnappa Chidambaraswamy <manukc at gmail.com>
Co-authored-by: Manohar Krishnappa Chidambaraswamy <manukc at gmail.com>
Signed-off-by: Vishal Deep Ajmera <vishal.deep.ajmera at ericsson.com>

CC: Jan Scheurich <jan.scheurich at ericsson.com>
CC: Venkatesan Pradeep <venkatesan.pradeep at ericsson.com>
CC: Ben Pfaff <blp at ovn.org>
CC: Ilya Maximets <i.maximets at ovn.org>
CC: Ian Stokes <ian.stokes at intel.com>
CC: David Marchand <david.marchand at redhat.com>
CC: Matteo Croce <mcroce at redhat.com>
CC: Eelco Chaudron <echaudro at redhat.com>

Signed-off-by: Vishal Deep Ajmera <vishal.deep.ajmera at ericsson.com>
Signed-off-by: 0-day Robot <robot at bytheb.org>

View the changeset: https://github.com/ovsrobot/ovs/commit/ab451829b997

View the full build log and details: https://travis-ci.org/github/ovsrobot/ovs/builds/661121047?utm_medium=notification&utm_source=email

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