@@ -5,9 +5,22 @@ 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-c630015db082@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'.
@@ -47,9 +60,6 @@ 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
----------------
@@ -65,7 +75,6 @@ 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
-----------------------
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.odaki@daynix.com> --- docs/devel/ebpf_rss.rst | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)