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From: Akihiko Odaki <akihiko.odaki@daynix.com>
Date: Thu, 13 Mar 2025 15:55:37 +0900
Subject: [PATCH RFC v4 11/11] docs/devel/ebpf_rss.rst: Update for peer RSS
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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(-)
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 v=
irtqueues
by calculating packet hash. Usually every queue is processed then by a spe=
cific guest CPU core.
=20
-For now there are 2 RSS implementations in qemu:
-- 'in-qemu' RSS (functions if qemu receives network packets, i.e. vhost=3D=
off)
-- eBPF RSS (can function with also with vhost=3Don)
+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 implemen=
t RSS.
+Currently QEMU can use the RSS implementation of vDPA and Linux's TUN modu=
le
+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.
=20
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
=20
tap,vhost=3Don & virtio-net-pci,rss=3Don,hash=3Don
=20
-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 l=
oad or set to TUN.
-
RSS eBPF program
----------------
=20
@@ -67,7 +77,6 @@ Prerequisites to recompile the eBPF program (regenerate e=
bpf/rss.bpf.skeleton.h)
$ make -f Makefile.ebpf
=20
Current eBPF RSS implementation uses 'bounded loops' with 'backward jump i=
nstructions' which present in the last kernels.
-Overall eBPF RSS works on kernels 5.8+.
=20
eBPF RSS implementation
-----------------------
--=20
2.48.1