| Message ID | 20230517031134.2756998-2-mkp@redhat.com |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | Enhanced checksum support | expand |
| Context | Check | Description |
|---|---|---|
| ovsrobot/apply-robot | success | apply and check: success |
| ovsrobot/github-robot-_Build_and_Test | success | github build: passed |
| ovsrobot/intel-ovs-compilation | success | test: success |
On 5/17/23 05:11, Mike Pattrick wrote: > From: Flavio Leitner <fbl@sysclose.org> > > Document the implementation of netdev hardware offloading > in userspace datapath. > > Signed-off-by: Flavio Leitner <fbl@sysclose.org> > Co-authored-by: Mike Pattrick <mkp@redhat.com> > Signed-off-by: Mike Pattrick <mkp@redhat.com> > --- > Since v9: > - Renamed documentation to reflect the userspace checksum nature of > this feature > - Edited for formatting and clarity issues. > Since v10: > - No change > Since v11: > - Modified document in accordance with Ilya's feedback > --- > Documentation/automake.mk | 1 + > Documentation/topics/index.rst | 1 + > .../topics/userspace-checksum-offloading.rst | 97 +++++++++++++++++++ > 3 files changed, 99 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..8157c25ea > --- /dev/null > +++ b/Documentation/topics/userspace-checksum-offloading.rst > @@ -0,0 +1,97 @@ > +.. > + 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. I can't make sense from this sentence. In a way that the status is not known? Sounds strange. Maybe break it down into 2-3 simpler ones? > + > +The interface (internally referred to as a netdev) can set flags indicating > +whether each packet's checksum is good or bad upon recipt. The checksum is s/recipt/receipt/ > +considered unverified if no flag is set. > + > +When packets ingress into the datapath with good checksum, OVS should postpone > +checksum updates for these packets until they egress. > + > +When a packet egress the datapath, the packet flags and the egress interface > +flags are verified to make sure all required offload features to send out the > +packet are available on the egress interface. 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.
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..8157c25ea --- /dev/null +++ b/Documentation/topics/userspace-checksum-offloading.rst @@ -0,0 +1,97 @@ +.. + 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. + +The interface (internally referred to as a netdev) can set flags indicating +whether each packet's checksum is good or bad upon recipt. The checksum is +considered unverified if no flag is set. + +When packets ingress into the datapath with good checksum, OVS should postpone +checksum updates for these packets until they egress. + +When a packet egress the datapath, the packet flags and the egress interface +flags are verified to make sure all required offload features to send out the +packet are available on the egress interface. 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.