On 2020/11/3 下午6:32, Yuri Benditovich wrote:
On Tue, Nov 3, 2020 at 11:02 AM Jason Wang <jasow...@redhat.com
<mailto:jasow...@redhat.com>> wrote:
On 2020/11/3 上午2:51, Andrew Melnychenko wrote:
> Basic idea is to use eBPF to calculate and steer packets in TAP.
> RSS(Receive Side Scaling) is used to distribute network packets
to guest virtqueues
> by calculating packet hash.
> eBPF RSS allows us to use RSS with vhost TAP.
>
> This set of patches introduces the usage of eBPF for packet steering
> and RSS hash calculation:
> * RSS(Receive Side Scaling) is used to distribute network packets to
> guest virtqueues by calculating packet hash
> * eBPF RSS suppose to be faster than already existing 'software'
> implementation in QEMU
> * Additionally adding support for the usage of RSS with vhost
>
> Supported kernels: 5.8+
>
> Implementation notes:
> Linux TAP TUNSETSTEERINGEBPF ioctl was used to set the eBPF program.
> Added eBPF support to qemu directly through a system call, see the
> bpf(2) for details.
> The eBPF program is part of the qemu and presented as an array
of bpf
> instructions.
> The program can be recompiled by provided Makefile.ebpf(need to
adjust
> 'linuxhdrs'),
> although it's not required to build QEMU with eBPF support.
> Added changes to virtio-net and vhost, primary eBPF RSS is used.
> 'Software' RSS used in the case of hash population and as a
fallback option.
> For vhost, the hash population feature is not reported to the guest.
>
> Please also see the documentation in PATCH 6/6.
>
> I am sending those patches as RFC to initiate the discussions
and get
> feedback on the following points:
> * Fallback when eBPF is not supported by the kernel
Yes, and it could also a lacking of CAP_BPF.
> * Live migration to the kernel that doesn't have eBPF support
Is there anything that we needs special treatment here?
Possible case: rss=on, vhost=on, source system with kernel 5.8
(everything works) -> dest. system 5.6 (bpf does not work), the
adapter functions, but all the steering does not use proper queues.
Right, I think we need to disable vhost on dest.
> * Integration with current QEMU build
Yes, a question here:
1) Any reason for not using libbpf, e.g it has been shipped with some
distros
We intentionally do not use libbpf, as it present only on some distros.
We can switch to libbpf, but this will disable bpf if libbpf is not
installed
That's better I think.
2) It would be better if we can avoid shipping bytecodes
This creates new dependencies: llvm + clang + ...
We would prefer byte code and ability to generate it if prerequisites
are installed.
It's probably ok if we treat the bytecode as a kind of firmware.
But in the long run, it's still worthwhile consider the qemu source is
used for development and llvm/clang should be a common requirement for
generating eBPF bytecode for host.
> * Additional usage for eBPF for packet filtering
Another interesting topics in to implement mac/vlan filters. And
in the
future, I plan to add mac based steering. All of these could be
done via
eBPF.
No problem, we can cooperate if needed
>
> Know issues:
> * hash population not supported by eBPF RSS: 'software' RSS used
Is this because there's not way to write to vnet header in
STERRING BPF?
Yes. We plan to submit changes for kernel to cooperate with BPF and
populate the hash, this work is in progress
That would require a new type of eBPF program and may need some work on
verifier.
Btw, macvtap is still lacking even steering ebpf program. Would you want
to post a patch to support that?
> as a fallback, also, hash population feature is not reported to
guests
> with vhost.
> * big-endian BPF support: for now, eBPF is disabled for
big-endian systems.
Are there any blocker for this?
No, can be added in v2
Cool.
Thanks
Just some quick questions after a glance of the codes. Will go
through
them tomorrow.
Thanks
>
> Andrew (6):
> Added SetSteeringEBPF method for NetClientState.
> ebpf: Added basic eBPF API.
> ebpf: Added eBPF RSS program.
> ebpf: Added eBPF RSS loader.
> virtio-net: Added eBPF RSS to virtio-net.
> docs: Added eBPF documentation.
>
> MAINTAINERS | 6 +
> configure | 36 +++
> docs/ebpf.rst | 29 ++
> docs/ebpf_rss.rst | 129 ++++++++
> ebpf/EbpfElf_to_C.py | 67 ++++
> ebpf/Makefile.ebpf | 38 +++
> ebpf/ebpf-stub.c | 28 ++
> ebpf/ebpf.c | 107 +++++++
> ebpf/ebpf.h | 35 +++
> ebpf/ebpf_rss.c | 178 +++++++++++
> ebpf/ebpf_rss.h | 30 ++
> ebpf/meson.build | 1 +
> ebpf/rss.bpf.c | 470 ++++++++++++++++++++++++++++
> ebpf/trace-events | 4 +
> ebpf/trace.h | 2 +
> ebpf/tun_rss_steering.h | 556
+++++++++++++++++++++++++++++++++
> hw/net/vhost_net.c | 2 +
> hw/net/virtio-net.c | 120 ++++++-
> include/hw/virtio/virtio-net.h | 4 +
> include/net/net.h | 2 +
> meson.build | 3 +
> net/tap-bsd.c | 5 +
> net/tap-linux.c | 19 ++
> net/tap-solaris.c | 5 +
> net/tap-stub.c | 5 +
> net/tap.c | 9 +
> net/tap_int.h | 1 +
> net/vhost-vdpa.c | 2 +
> 28 files changed, 1889 insertions(+), 4 deletions(-)
> create mode 100644 docs/ebpf.rst
> create mode 100644 docs/ebpf_rss.rst
> create mode 100644 ebpf/EbpfElf_to_C.py
> create mode 100755 ebpf/Makefile.ebpf
> create mode 100644 ebpf/ebpf-stub.c
> create mode 100644 ebpf/ebpf.c
> create mode 100644 ebpf/ebpf.h
> create mode 100644 ebpf/ebpf_rss.c
> create mode 100644 ebpf/ebpf_rss.h
> create mode 100644 ebpf/meson.build
> create mode 100644 ebpf/rss.bpf.c
> create mode 100644 ebpf/trace-events
> create mode 100644 ebpf/trace.h
> create mode 100644 ebpf/tun_rss_steering.h
>
