eBPF RSS virtio-net support was written in assumption that there is only one alternative RSS implementation: 'in-qemu' RSS. It is no longer true, and we now have yet another implementation; namely the peer RSS.
Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com> --- docs/devel/ebpf_rss.rst | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) diff --git a/docs/devel/ebpf_rss.rst b/docs/devel/ebpf_rss.rst index ed5d33767bd5..f128f0990905 100644 --- a/docs/devel/ebpf_rss.rst +++ b/docs/devel/ebpf_rss.rst @@ -7,9 +7,22 @@ eBPF RSS virtio-net support RSS(Receive Side Scaling) is used to distribute network packets to guest virtqueues by calculating packet hash. Usually every queue is processed then by a specific guest CPU core. -For now there are 2 RSS implementations in qemu: -- 'in-qemu' RSS (functions if qemu receives network packets, i.e. vhost=off) -- eBPF RSS (can function with also with vhost=on) +For now there are 3 RSS implementations in qemu: +1. Peer RSS +2. eBPF RSS +3. 'In-QEMU' RSS + +'In-QEMU' RSS is incompatible with vhost since the packets are not routed to +QEMU. eBPF RSS requires Linux 5.8+. Peer RSS requires the peer to implement RSS. +Currently QEMU can use the RSS implementation of vDPA and Linux's TUN module +with the following patch applied: +https://lore.kernel.org/r/20240915-rss-v3-0-c630015db...@daynix.com/ + +eBPF RSS does not support hash reporting. Peer RSS may support limited hash +types. + +virtio-net automatically chooses the RSS implementation to use. Peer RSS is +the most preferred, and 'in-QEMU' RSS is the least. eBPF support (CONFIG_EBPF) is enabled by 'configure' script. To enable eBPF RSS support use './configure --enable-bpf'. @@ -49,9 +62,6 @@ eBPF RSS turned on by different combinations of vhost-net, vitrio-net and tap co tap,vhost=on & virtio-net-pci,rss=on,hash=on -If CONFIG_EBPF is not set then only 'in-qemu' RSS is supported. -Also 'in-qemu' RSS, as a fallback, is used if the eBPF program failed to load or set to TUN. - RSS eBPF program ---------------- @@ -67,7 +77,6 @@ Prerequisites to recompile the eBPF program (regenerate ebpf/rss.bpf.skeleton.h) $ make -f Makefile.ebpf Current eBPF RSS implementation uses 'bounded loops' with 'backward jump instructions' which present in the last kernels. -Overall eBPF RSS works on kernels 5.8+. eBPF RSS implementation ----------------------- -- 2.48.1
