Jason Wang <jasow...@redhat.com> writes: > 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. > > > Adding Toke for sharing more idea from eBPF side. > > We had some discussion on the eBPF issues: > > 1) Whether or not to use libbpf. Toke strongly suggest to use libbpf > 2) Whether or not to use BTF. Toke confirmed that if we don't access any > skb metadata, BTF is not strictly required for CO-RE. But it might still > useful for e.g debugging. > 3) About the huge (5K lines, see patch #2 Toke). Toke confirmed that we > can strip debug symbols, but Yuri found some sections can't be stripped, > we can keep discussing here.
I just tried simply running 'strip' on a sample trivial XDP program, which brought its size down from ~5k to ~1k and preserved the BTF information without me having to do anything. As a side note, though, instead of embedding the BPF program into a .h, you could simply ship it as a .o and load it from the file system. We do that with xdp-tools and install the bpf object files into /usr/$LIB/bpf/. -Toke
