[RFC PATCH net-next v1 1/2] net: add SO_NO_RFS to exclude a socket from RFS and aRFS
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HOTtoday
From: Vitaly Zuevsky <hidden>
Date: 2026-10-31 11:33:36
Also in:
linux-alpha, linux-arch, linux-doc, linux-mips, lkml, sparclinux
Subsystem:
alpha port, generic include/asm header files, mips, networking [general], networking [sockets], parisc architecture, sparc + ultrasparc (sparc/sparc64), the rest · Maintainers:
Richard Henderson, Matt Turner, Magnus Lindholm, Arnd Bergmann, Thomas Bogendoerfer, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Kuniyuki Iwashima, Willem de Bruijn, "James E.J. Bottomley", Helge Deller, Andreas Larsson, Linus Torvalds
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 <redacted> --- 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