On Wed, Nov 04, 2020 at 10:07:52AM +0800, Jason Wang wrote: > > 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.
That is explicitly *not* OK for inclusion in Fedora. They require that BPF is compiled from source, and rejected my suggestion that it could be considered a kind of firmware and thus have an exception from building from source. > 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. So we need to do this right straight way before this merges. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
