On 2020/11/26 下午8:52, Yuri Benditovich wrote:
>
>
> On Mon, Nov 23, 2020 at 8:08 AM Jason Wang <jasowang@redhat.com
> <mailto:jasowang@redhat.com>> wrote:
>
>
> 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
>
>
> After some experiments we can see that stripping of debug sections
> reduces the size of
> ELF from ~45K to ~20K (we tried to strip more but the libbpf fails to
> load it, libbpf needs BTF and symbols)
> So I suggest to reevaluate the necessity of libbpf.
> For this specific BPF it does not present advantage and we hardly can
> create some reusable code
> related to libbpf, i.e. any further BPF will need its own libbpf wrapper.
> The BTF is really good feature and in case some later BPF will need an
> access to kernel
> structures it will use libbpf loader.
> What you think about it?
If we can find a way to use BTF without libbpf, it should be acceptable.
But the point is that the RSS BPF does not need the BTF as it does not use any kernel structures.
When we have, for example, filter BPF that will need the BTF - we'll use libbpf for it.
Anyway we do not have here any infrastructural code related to libbpf,
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
> >
>