Re: [RFC PATCH v2 0/5] eBPF RSS support for virtio-net

[Jason Wang <jasowang@redhat.com>]

On 2020/11/19 下午7:13, Andrew Melnychenko wrote:
> 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
> * Additionally adding support for the usage of RSS with vhost
>
> The eBPF works on kernels 5.8+
> On earlier kerneld it fails to load and the RSS feature is reported
> only without vhost and implemented in 'in-qemu' software.
>
> Implementation notes:
> Linux TAP TUNSETSTEERINGEBPF ioctl was used to set the eBPF program.
> Added libbpf dependency and eBPF support.
> The eBPF program is part of the qemu and presented as an array
> of BPF ELF file data.
> The compilation of eBPF is not part of QEMU build and can be done
> using provided Makefile.ebpf(need to adjust 'linuxhdrs').
> Added changes to virtio-net and vhost, primary eBPF RSS is used.
> 'in-qemu' 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 5/5.
>
> 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
> * Live migration to the kernel that doesn't have eBPF support
> * Integration with current QEMU build
> * Additional usage for eBPF for packet filtering
>
> Known issues:
> * hash population not supported by eBPF RSS: 'in-qemu' RSS used
> as a fallback, also, hash population feature is not reported to guests
> with vhost.
> * big-endian BPF support: for now, eBPF isn't supported on
> big-endian systems. Can be added in future if required.
> * huge .h file with eBPF binary. The size of .h file containing
> eBPF binary is currently ~5K lines, because the binary is built with debug information.
> The binary without debug/BTF info can't be loaded by libbpf.
> We're looking for possibilities to reduce the size of the .h files.


A question here, is this because the binary file contains DWARF data? If 
yes, is it a building or loading dependency? If it's latter, maybe we 
can try to strip them out, anyhow it can't be recognized by kernel.

Thanks


>
> Changes since v1:
> * using libbpf instead of direct 'bpf' system call.
> * added libbpf dependency to the configure/meson scripts.
> * changed python script for eBPF .h file generation.
> * changed eBPF program - reading L3 proto from ethernet frame.
> * added TUNSETSTEERINGEBPF define for TUN.
> * changed the maintainer's info.
> * added license headers.
> * refactored code.
>
> Andrew (5):
>    net: Added SetSteeringEBPF method for NetClientState.
>    ebpf: Added eBPF RSS program.
>    ebpf: Added eBPF RSS loader.
>    virtio-net: Added eBPF RSS to virtio-net.
>    docs: Added eBPF RSS documentation.
>
>   MAINTAINERS                    |    7 +
>   configure                      |   33 +
>   docs/ebpf_rss.rst              |  133 +
>   ebpf/EbpfElf_to_C.py           |   36 +
>   ebpf/Makefile.ebpf             |   33 +
>   ebpf/ebpf_rss-stub.c           |   40 +
>   ebpf/ebpf_rss.c                |  186 ++
>   ebpf/ebpf_rss.h                |   44 +
>   ebpf/meson.build               |    1 +
>   ebpf/rss.bpf.c                 |  505 +++
>   ebpf/tun_rss_steering.h        | 5439 ++++++++++++++++++++++++++++++++
>   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                    |   11 +
>   net/tap-bsd.c                  |    5 +
>   net/tap-linux.c                |   13 +
>   net/tap-linux.h                |    1 +
>   net/tap-solaris.c              |    5 +
>   net/tap-stub.c                 |    5 +
>   net/tap.c                      |    9 +
>   net/tap_int.h                  |    1 +
>   net/vhost-vdpa.c               |    2 +
>   24 files changed, 6633 insertions(+), 4 deletions(-)
>   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_rss-stub.c
>   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/tun_rss_steering.h
>