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
    >



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