This is a rough PoC for an idea to offload TC flower to XDP.
* Motivation
The purpose is to speed up software TC flower by using XDP.
I chose TC flower because my current interest is in OVS. OVS uses TC to
offload flow tables to hardware, so if TC can offload flows to XDP, OVS
also can be offloaded to XDP.
When TC flower filter is offloaded to XDP, the received packets are
handled by XDP first, and if their protocol or something is not
supported by the eBPF program, the program returns XDP_PASS and packets
are passed to upper layer TC.
The packet processing flow will be like this when this mechanism,
xdp_flow, is used with OVS.
+-------------+
| openvswitch |
| kmod |
+-------------+
^
| if not match in filters (flow key or action not supported by TC)
+-------------+
| TC flower |
+-------------+
^
| if not match in flow tables (flow key or action not supported by XDP)
+-------------+
| XDP prog |
+-------------+
^
| incoming packets
Of course we can directly use TC flower without OVS to speed up TC.
This is useful especially when the device does not support HW-offload.
Such interfaces include virtual interfaces like veth.
* How to use
It only supports ingress (clsact) flower filter at this point.
Enable the feature via ethtool before adding ingress/clsact qdisc.
$ ethtool -K eth0 tc-offload-xdp on
Then add qdisc/filters as normal.
$ tc qdisc add dev eth0 clsact
$ tc filter add dev eth0 ingress protocol ip flower skip_sw ...
Alternatively, when using OVS, adding qdisc and filters will be
automatically done by setting hw-offload.
$ ovs-vsctl set Open_vSwitch . other_config:hw-offload=true
$ systemctl stop openvswitch
$ tc qdisc del dev eth0 ingress # or reboot
$ ethtool -K eth0 tc-offload-xdp on
$ systemctl start openvswitch
* Performance
I measured drop rate at veth interface with redirect action from physical
interface (i40e 25G NIC, XXV 710) to veth. The CPU is Xeon Silver 4114
(2.20 GHz).
XDP_DROP
+------+ +-------+ +-------+
pktgen -- wire --> | eth0 | -- TC/OVS redirect --> | veth0 |----| veth1 |
+------+ (offloaded to XDP) +-------+ +-------+
The setup for redirect is done by OVS like this.
$ ovs-vsctl add-br ovsbr0
$ ovs-vsctl add-port ovsbr0 eth0
$ ovs-vsctl add-port ovsbr0 veth0
$ ovs-vsctl set Open_vSwitch . other_config:hw-offload=true
$ systemctl stop openvswitch
$ tc qdisc del dev eth0 ingress
$ tc qdisc del dev veth0 ingress
$ ethtool -K eth0 tc-offload-xdp on
$ ethtool -K veth0 tc-offload-xdp on
$ systemctl start openvswitch
Tested single core/single flow with 3 configurations.
- xdp_flow: hw-offload=true, tc-offload-xdp on
- TC: hw-offload=true, tc-offload-xdp off (software TC)
- ovs kmod: hw-offload=false
xdp_flow TC ovs kmod
-------- -------- --------
4.0 Mpps 1.1 Mpps 1.1 Mpps
So xdp_flow drop rate is roughly 4x faster than software TC or ovs kmod.
OTOH the time to add a flow increases with xdp_flow.
ping latency of first packet when veth1 does XDP_PASS instead of DROP:
xdp_flow TC ovs kmod
-------- -------- --------
25ms 12ms 0.6ms
xdp_flow does a lot of work to emulate TC behavior including UMH
transaction and multiple bpf map update from UMH which I think increases
the latency.
* Implementation
xdp_flow makes use of UMH to load an eBPF program for XDP, similar to
bpfilter. The difference is that xdp_flow does not generate the eBPF
program dynamically but a prebuilt program is embedded in UMH. This is
mainly because flow insertion is considerably frequent. If we generate
and load an eBPF program on each insertion of a flow, the latency of the
first packet of ping in above test will incease, which I want to avoid.
+----------------------+
| xdp_flow_umh | load eBPF prog for XDP
| (eBPF prog embedded) | update maps for flow tables
+----------------------+
^ |
request | v eBPF prog id
+-----------+ offload +-----------------------+
| TC flower | --------> | xdp_flow kmod | attach the prog to XDP
+-----------+ | (flow offload driver) |
+-----------------------+
- When ingress/clsact qdisc is created, i.e. a device is bound to a flow
block, xdp_flow kmod requests xdp_flow_umh to load eBPF prog.
xdp_flow_umh returns prog id and xdp_flow kmod attach the prog to XDP
(the reason of attaching XDP from kmod is that rtnl_lock is held here).
- When flower filter is added, xdp_flow kmod requests xdp_flow_umh to
update maps for flow tables.
* Patches
- patch 1
Basic framework for xdp_flow kmod and UMH.
- patch 2
Add prebuilt eBPF program embedded in UMH.
- patch 3, 4
Attach the prog to XDP in kmod after using the prog id returned from
UMH.
- patch 5, 6
Add maps for flow tables and flow table manipulation logic in UMH.
- patch 7
Implement flow lookup and basic actions in eBPF prog.
- patch 8
Implement flow manipulation logic, serialize flow key and actions from
TC flower and make requests to UMH in kmod.
- patch 9
Add tc-offload-xdp netdev feature and hooks to call xdp_flow kmod in
TC flower offload code.
- patch 10, 11
Add example actions, redirect and vlan_push.
- patch 12
Add testcase for xdp_flow.
- patch 13, 14
These are unrelated patches. They just improves XDP program's
performance. They are included to demonstrate to what extent xdp_flow
performance can increase. Without them, drop rate goes down from 4Mpps
to 3Mpps.
* About OVS AF_XDP netdev
Recently OVS has added AF_XDP netdev type support. This also makes use
of XDP, but in some ways different from this patch set.
- AF_XDP work originally started in order to bring BPF's flexibility to
OVS, which enables us to upgrade datapath without updating kernel.
AF_XDP solution uses userland datapath so it achieved its goal.
xdp_flow will not replace OVS datapath completely, but offload it
partially just for speed up.
- OVS AF_XDP requires PMD for the best performance so consumes 100% CPU.
- OVS AF_XDP needs packet copy when forwarding packets.
- xdp_flow can be used not only for OVS. It works for direct use of TC
flower. nftables also can be offloaded by the same mechanism in the
future.
* About alternative userland (ovs-vswitchd etc.) implementation
Maybe a similar logic can be implemented in ovs-vswitchd offload
mechanism, instead of adding code to kernel. I just thought offloading
TC is more generic and allows wider usage with direct TC command.
For example, considering that OVS inserts a flow to kernel only when
flow miss happens in kernel, we can in advance add offloaded flows via
tc filter to avoid flow insertion latency for certain sensitive flows.
TC flower usage without using OVS is also possible.
Also as written above nftables can be offloaded to XDP with this
mechanism as well.
* Note
This patch set is based on top of commit a664a834579a ("tools: bpftool:
fix reading from /proc/config.gz").
Any feedback is welcome.
Thanks!
Signed-off-by: Toshiaki Makita <toshiaki.makita1@xxxxxxxxx>
Toshiaki Makita (14):
xdp_flow: Add skeleton of XDP based TC offload driver
xdp_flow: Add skeleton bpf program for XDP
bpf: Add API to get program from id
xdp_flow: Attach bpf prog to XDP in kernel after UMH loaded program
xdp_flow: Prepare flow tables in bpf
xdp_flow: Add flow entry insertion/deletion logic in UMH
xdp_flow: Add flow handling and basic actions in bpf prog
xdp_flow: Implement flow replacement/deletion logic in xdp_flow kmod
xdp_flow: Add netdev feature for enabling TC flower offload to XDP
xdp_flow: Implement redirect action
xdp_flow: Implement vlan_push action
bpf, selftest: Add test for xdp_flow
i40e: prefetch xdp->data before running XDP prog
bpf, hashtab: Compare keys in long
drivers/net/ethernet/intel/i40e/i40e_txrx.c | 1 +
include/linux/bpf.h | 6 +
include/linux/netdev_features.h | 2 +
include/linux/netdevice.h | 4 +
include/net/flow_offload_xdp.h | 33 +
include/net/pkt_cls.h | 5 +
include/net/sch_generic.h | 1 +
kernel/bpf/hashtab.c | 27 +-
kernel/bpf/syscall.c | 26 +-
net/Kconfig | 1 +
net/Makefile | 1 +
net/core/dev.c | 13 +-
net/core/ethtool.c | 1 +
net/sched/cls_api.c | 67 +-
net/xdp_flow/.gitignore | 1 +
net/xdp_flow/Kconfig | 16 +
net/xdp_flow/Makefile | 112 +++
net/xdp_flow/msgfmt.h | 102 +++
net/xdp_flow/umh_bpf.h | 34 +
net/xdp_flow/xdp_flow_core.c | 126 ++++
net/xdp_flow/xdp_flow_kern_bpf.c | 358 +++++++++
net/xdp_flow/xdp_flow_kern_bpf_blob.S | 7 +
net/xdp_flow/xdp_flow_kern_mod.c | 645 ++++++++++++++++
net/xdp_flow/xdp_flow_umh.c | 1034 ++++++++++++++++++++++++++
net/xdp_flow/xdp_flow_umh_blob.S | 7 +
tools/testing/selftests/bpf/Makefile | 1 +
tools/testing/selftests/bpf/test_xdp_flow.sh | 103 +++
27 files changed, 2716 insertions(+), 18 deletions(-)
create mode 100644 include/net/flow_offload_xdp.h
create mode 100644 net/xdp_flow/.gitignore
create mode 100644 net/xdp_flow/Kconfig
create mode 100644 net/xdp_flow/Makefile
create mode 100644 net/xdp_flow/msgfmt.h
create mode 100644 net/xdp_flow/umh_bpf.h
create mode 100644 net/xdp_flow/xdp_flow_core.c
create mode 100644 net/xdp_flow/xdp_flow_kern_bpf.c
create mode 100644 net/xdp_flow/xdp_flow_kern_bpf_blob.S
create mode 100644 net/xdp_flow/xdp_flow_kern_mod.c
create mode 100644 net/xdp_flow/xdp_flow_umh.c
create mode 100644 net/xdp_flow/xdp_flow_umh_blob.S
create mode 100755 tools/testing/selftests/bpf/test_xdp_flow.sh
--
1.8.3.1
