On Tue, Aug 13, 2019 at 5:07 AM Toshiaki Makita
<toshiaki.makita1@xxxxxxxxx> wrote:
>
> 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
>
I like this idea, some comments about the OVS AF_XDP work.
Another way when using OVS AF_XDP is to serve as slow path of TC flow
HW offload.
For example:
Userspace OVS datapath (The one used by OVS-DPDK)
^
|
+------------------------------+
| OVS AF_XDP netdev |
+------------------------------+
^
| if not supported or not match in flow tables
+---------------------+
| TC HW flower |
+---------------------+
^
| incoming packets
So in this case it's either TC HW flower offload, or the userspace PMD OVS.
Both cases should be pretty fast.
I think xdp_flow can also be used by OVS AF_XDP netdev, sitting between
TC HW flower and OVS AF_XDP netdev.
Before the XDP program sending packet to AF_XDP socket, the
xdp_flow can execute first, and if not match, then send to AF_XDP.
So in your patch set, implement s.t like
bpf_redirect_map(&xsks_map, index, 0);
Another thing is that at each layer we are doing its own packet parsing.
>From your graph, first parse at XDP program, then at TC flow, then at
openvswitch kmod.
I wonder if we can reuse some parsing result.
Regards,
William
> 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
>
