Re: [RFC PATCH 0/6] eBPF RSS support for virtio-net

[Jason Wang]

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?


> * 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
2) It would be better if we can avoid shipping bytecodes


> * 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.


> 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?


> 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?

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