Re: [RFC PATCH v3 0/6] eBPF RSS support for virtio-net

[Jason Wang <jasowang@redhat.com>]

On 2021/1/15 上午5:16, 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 eBPF array file initially generated by bpftool.
> 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 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
> * 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.


Looks good overall. I think a formal series could be posted for the next 
version.

Please see comments in the patch and I think we need to add a migration 
blocker if RSS is supported by virtio-net. (And implement migration in 
the future).

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.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.
>
> Changes since v2:
> * using bpftool for eBPF skeleton generation.
> * ebpf_rss is refactored to use skeleton generated by bpftool.
> * added/adjasted license in comment sections and in eBPF file.
> * rss.bpf.c and Makefile.ebpf moved to the tool/ebpf folder.
> * virtio-net eBPF rss refactored. Now eBPF initialized during realize().
>
> Andrew (6):
>    net/tap: Added TUNSETSTEERINGEBPF code.
>    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 documentation.
>
>   MAINTAINERS                    |   8 +
>   configure                      |  33 +++
>   docs/ebpf_rss.rst              | 125 ++++++++
>   ebpf/ebpf_rss-stub.c           |  40 +++
>   ebpf/ebpf_rss.c                | 165 +++++++++++
>   ebpf/ebpf_rss.h                |  44 +++
>   ebpf/meson.build               |   1 +
>   ebpf/rss.bpf.skeleton.h        | 397 ++++++++++++++++++++++++++
>   ebpf/trace-events              |   4 +
>   ebpf/trace.h                   |   2 +
>   hw/net/vhost_net.c             |   2 +
>   hw/net/virtio-net.c            | 125 +++++++-
>   include/hw/virtio/virtio-net.h |   4 +
>   include/net/net.h              |   2 +
>   meson.build                    |  13 +
>   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 +
>   tools/ebpf/Makefile.ebpf       |  33 +++
>   tools/ebpf/rss.bpf.c           | 505 +++++++++++++++++++++++++++++++++
>   25 files changed, 1540 insertions(+), 4 deletions(-)
>   create mode 100644 docs/ebpf_rss.rst
>   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.skeleton.h
>   create mode 100644 ebpf/trace-events
>   create mode 100644 ebpf/trace.h
>   create mode 100755 tools/ebpf/Makefile.ebpf
>   create mode 100644 tools/ebpf/rss.bpf.c
>