[RFC PATCH net-next v1 1/2] net: add SO_NO_RFS to exclude a socket from RFS and aRFS
From: Vitaly Zuevsky
Date: Sat Oct 31 2026 - 07:34:04 EST
RFS and accelerated RFS are enabled per host and per rx queue, but
whether steering helps is a property of the flow. A host that carries
a few long-lived flows which benefit from steering alongside a large
churn of short-lived flows has no way to express that today.
Add a boolean socket option, SO_NO_RFS. When set, sock_rps_record_flow()
does not record the socket in rps_sock_flow_table, so get_rps_cpu()
finds no match and neither software RFS nor ndo_rx_flow_steer() acts
on the flow; it stays on the CPU chosen by RSS or RPS.
The option is kept in sk_flags so that sk_clone_lock() copies it to
accepted children: setting it on a listening socket excludes every
connection accepted from it, while sockets the same process connects
itself remain eligible.
sock_rps_delete_flow() is skipped as well, because a socket that never
recorded itself must not clear a table slot that may belong to another
flow.
The test sits after the TCP_ESTABLISHED check and inside the
rfs_needed static branch, so hosts without RFS pay nothing and hosts
with RFS pay one test_bit() on a cache line tcp_recvmsg() already
touches.
Signed-off-by: Vitaly Zuevsky <vitaly.zuevsky@xxxxxxxxx>
---
arch/alpha/include/uapi/asm/socket.h | 2 ++
arch/mips/include/uapi/asm/socket.h | 2 ++
arch/parisc/include/uapi/asm/socket.h | 2 ++
arch/sparc/include/uapi/asm/socket.h | 2 ++
include/net/rps.h | 13 +++++++++++++
include/net/sock.h | 1 +
include/uapi/asm-generic/socket.h | 2 ++
net/core/sock.c | 8 ++++++++
8 files changed, 32 insertions(+)
diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index 5d3524c26b2b..256d37f5b9b0 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -161,6 +161,8 @@
#define SO_PEERPIDFD_THREAD 87
+#define SO_NO_RFS 88
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 245a43f52fb1..5b477de463a3 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -172,6 +172,8 @@
#define SO_PEERPIDFD_THREAD 87
+#define SO_NO_RFS 88
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index f23710e1c671..b3a4cc2cbc50 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -153,6 +153,8 @@
#define SO_PEERPIDFD_THREAD 0x4055
+#define SO_NO_RFS 0x4056
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index b35b25bdefc2..ba5ed7942570 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -154,6 +154,8 @@
#define SO_PEERPIDFD_THREAD 0x0060
+#define SO_NO_RFS 0x0061
+
#if !defined(__KERNEL__)
diff --git a/include/net/rps.h b/include/net/rps.h
index e33c6a2fa8bb..5afa48868236 100644
--- a/include/net/rps.h
+++ b/include/net/rps.h
@@ -98,6 +98,13 @@ static inline void _sock_rps_record_flow(const struct sock *sk)
* [1] : sk_state and sk_prot are in the same cache line.
*/
if (sk->sk_state == TCP_ESTABLISHED) {
+ /* SO_NO_RFS: application asked us to never steer this flow.
+ * Tested after sk_state so the common case stays on one
+ * cache line.
+ */
+ if (unlikely(sock_flag(sk, SOCK_NO_RFS)))
+ return;
+
/* This READ_ONCE() is paired with the WRITE_ONCE()
* from sock_rps_save_rxhash() and sock_rps_reset_rxhash().
*/
@@ -111,6 +118,12 @@ static inline void _sock_rps_delete_flow(const struct sock *sk)
rps_tag_ptr tag_ptr;
u32 hash, index;
+ /* Never recorded, so never clear a slot that may belong to
+ * another flow.
+ */
+ if (sock_flag(sk, SOCK_NO_RFS))
+ return;
+
hash = READ_ONCE(sk->sk_rxhash);
if (!hash)
return;
diff --git a/include/net/sock.h b/include/net/sock.h
index 173b37b2b8bb..4472dc4ed28e 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1024,6 +1024,7 @@ enum sock_flags {
SOCK_RCVMARK, /* Receive SO_MARK ancillary data with packet */
SOCK_RCVPRIORITY, /* Receive SO_PRIORITY ancillary data with packet */
SOCK_TIMESTAMPING_ANY, /* Copy of sk_tsflags & TSFLAGS_ANY */
+ SOCK_NO_RFS, /* SO_NO_RFS: never record this flow for RFS/aRFS */
};
#define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 56fed7ab27ab..9bf415b0d470 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -156,6 +156,8 @@
#define SO_PEERPIDFD_THREAD 87
+#define SO_NO_RFS 88
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/sock.c b/net/core/sock.c
index e7405be8941f..02b8cc4bc1c4 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1597,6 +1597,10 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
reuseport_update_incoming_cpu(sk, val);
break;
+ case SO_NO_RFS:
+ sock_valbool_flag(sk, SOCK_NO_RFS, valbool);
+ break;
+
case SO_CNX_ADVICE:
if (val == 1)
dst_negative_advice(sk);
@@ -2118,6 +2122,10 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
v.val = READ_ONCE(sk->sk_incoming_cpu);
break;
+ case SO_NO_RFS:
+ v.val = sock_flag(sk, SOCK_NO_RFS);
+ break;
+
case SO_MEMINFO:
{
u32 meminfo[SK_MEMINFO_VARS];
base-commit: 734bef548a96e8774d6eef5dfa2026c6edc4e80b
--
2.34.1