From: Flavio Leitner <[email protected]> Document the implementation of netdev hardware offloading in userspace datapath.
Signed-off-by: Flavio Leitner <[email protected]> Co-authored-by: Mike Pattrick <[email protected]> Signed-off-by: Mike Pattrick <[email protected]> --- Since v9: - Renamed documentation to reflect the userspace checksum nature of this feature - Edited for formatting and clarity issues. Since v10: - No change --- Documentation/automake.mk | 1 + Documentation/topics/index.rst | 1 + .../topics/userspace-checksum-offloading.rst | 103 ++++++++++++++++++ 3 files changed, 105 insertions(+) create mode 100644 Documentation/topics/userspace-checksum-offloading.rst diff --git a/Documentation/automake.mk b/Documentation/automake.mk index cdf3c9926..8bd3dbb2b 100644 --- a/Documentation/automake.mk +++ b/Documentation/automake.mk @@ -57,6 +57,7 @@ DOC_SOURCE = \ Documentation/topics/record-replay.rst \ Documentation/topics/tracing.rst \ Documentation/topics/usdt-probes.rst \ + Documentation/topics/userspace-checksum-offloading.rst \ Documentation/topics/userspace-tso.rst \ Documentation/topics/userspace-tx-steering.rst \ Documentation/topics/windows.rst \ diff --git a/Documentation/topics/index.rst b/Documentation/topics/index.rst index 90d4c66e6..f239fcf83 100644 --- a/Documentation/topics/index.rst +++ b/Documentation/topics/index.rst @@ -55,5 +55,6 @@ OVS userspace-tso idl-compound-indexes ovs-extensions + userspace-checksum-offloading userspace-tx-steering usdt-probes diff --git a/Documentation/topics/userspace-checksum-offloading.rst b/Documentation/topics/userspace-checksum-offloading.rst new file mode 100644 index 000000000..7ab258710 --- /dev/null +++ b/Documentation/topics/userspace-checksum-offloading.rst @@ -0,0 +1,103 @@ +.. + Licensed under the Apache License, Version 2.0 (the "License"); you may + not use this file except in compliance with the License. You may obtain + a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, WITHOUT + WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the + License for the specific language governing permissions and limitations + under the License. + + Convention for heading levels in Open vSwitch documentation: + + ======= Heading 0 (reserved for the title in a document) + ------- Heading 1 + ~~~~~~~ Heading 2 + +++++++ Heading 3 + ''''''' Heading 4 + + Avoid deeper levels because they do not render well. + +======================================== +Userspace Datapath - Checksum Offloading +======================================== + +This document explains the internals of Open vSwitch support for checksum +offloading in the userspace datapath. + +Design +------ + +Open vSwitch strives to forward packets as they arrive regardless of whether +the checksum is correct or not. OVS is not responsible for fixing external +checksum issues. + +The checksum calculation can be offloaded to the NIC when the packet's checksum +is verified, known to be good, or known to be destined for an interface that +will recalculate the checksum anyways. + +In other cases, OVS will update the checksum if packet contents is modified in +a way that would also invalidate the checksum and the checksum status is not +known. + +For example, OVS can accept a packet with a corrupted IP checksum, and a flow +rule can change the IP destination address to another address. In that case, +OVS needs to partially recompute the checksum instead of offloading or +calculate all of it again which would fix the existing issue. + +The interface (internally referred to as a netdev) can set flags indicating if +the checksum is good or bad. The checksum is considered unverified if no flag +is set. + +When packets ingress into the datapath with good checksum, OVS should enable +checksum offload by default. This allows the data path to postpone checksum +updates until the packet egress the data path. + +When a packet egress the datapath, the packet flags and the egress interface +flags are verified to make sure all required NIC offload features to send out +the packet are available. If not, the data path will fall back to equivalent +software implementation. + + +Interface (a.k.a. Netdev) +------------------------- + +When the interface initiates, it should set the flags to tell the datapath +which offload features are supported. For example, if the driver supports IP +checksum offloading, then netdev->ol_flags should set the flag +NETDEV_TX_OFFLOAD_IPV4_CKSUM. + + +Rules +----- + +1) OVS should strive to forward all packets regardless of checksum. + +2) OVS must not correct a bad packet checksum. + +3) Packet with flag DP_PACKET_OL_RX_IP_CKSUM_GOOD means that the IP checksum is + present in the packet and it is good. + +4) Packet with flag DP_PACKET_OL_RX_IP_CKSUM_BAD means that the IP checksum is + present in the packet and it is bad. Extra care should be taken to not fix + the packet during data path processing. + +5) The ingress packet parser can only set DP_PACKET_OL_TX_IP_CKSUM if the + packet has DP_PACKET_OL_RX_IP_CKSUM_GOOD to not violate rule #2. + +6) Packet with flag DP_PACKET_OL_TX_IPV4 is an IPv4 packet. + +7) Packet with flag DP_PACKET_OL_TX_IPV6 is an IPv6 packet. + +8) Packet with flag DP_PACKET_OL_TX_IP_CKSUM tells the datapath to skip + updating the IP checksum if the packet is modified. The IP checksum will be + calculated by the egress interface if that supports IP checksum offload, + otherwise the IP checksum will be performed in software before handing over + the packet to the interface. + +9) When there are modifications to the packet that requires a checksum update, + the datapath needs to remove the DP_PACKET_OL_RX_IP_CKSUM_GOOD flag, + otherwise the checksum is assumed to be good in the packet. -- 2.31.1 _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
