From 4effb335b5dab08cb6e2c38d038910f8b527cfc9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 16 Sep 2025 16:09:48 +0000 Subject: [PATCH] net: group sk_backlog and sk_receive_queue UDP receivers suffer from sk_rmem_alloc updates, currently sharing a cache line with fields that need to be read-mostly (sock_read_rx group): 1) RFS enabled hosts read sk_napi_id from __udpv6_queue_rcv_skb(). 2) sk->sk_rcvbuf is read from __udp_enqueue_schedule_skb() /* --- cacheline 3 boundary (192 bytes) --- */ struct { atomic_t rmem_alloc; /* 0xc0 0x4 */ // Oops int len; /* 0xc4 0x4 */ struct sk_buff * head; /* 0xc8 0x8 */ struct sk_buff * tail; /* 0xd0 0x8 */ } sk_backlog; /* 0xc0 0x18 */ __u8 __cacheline_group_end__sock_write_rx[0]; /* 0xd8 0 */ __u8 __cacheline_group_begin__sock_read_rx[0]; /* 0xd8 0 */ struct dst_entry * sk_rx_dst; /* 0xd8 0x8 */ int sk_rx_dst_ifindex;/* 0xe0 0x4 */ u32 sk_rx_dst_cookie; /* 0xe4 0x4 */ unsigned int sk_ll_usec; /* 0xe8 0x4 */ unsigned int sk_napi_id; /* 0xec 0x4 */ u16 sk_busy_poll_budget;/* 0xf0 0x2 */ u8 sk_prefer_busy_poll;/* 0xf2 0x1 */ u8 sk_userlocks; /* 0xf3 0x1 */ int sk_rcvbuf; /* 0xf4 0x4 */ struct sk_filter * sk_filter; /* 0xf8 0x8 */ Move sk_error (which is less often dirtied) there. Alternative would be to cache align sock_read_rx but this has more implications/risks. Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Reviewed-by: David Ahern Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20250916160951.541279-8-edumazet@google.com Reviewed-by: Jakub Kicinski Signed-off-by: Paolo Abeni --- include/net/sock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/sock.h b/include/net/sock.h index 0fd4659353341..867dc44140d4c 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -394,7 +394,6 @@ struct sock { atomic_t sk_drops; __s32 sk_peek_off; - struct sk_buff_head sk_error_queue; struct sk_buff_head sk_receive_queue; /* * The backlog queue is special, it is always used with @@ -412,6 +411,7 @@ struct sock { } sk_backlog; #define sk_rmem_alloc sk_backlog.rmem_alloc + struct sk_buff_head sk_error_queue; __cacheline_group_end(sock_write_rx); __cacheline_group_begin(sock_read_rx); -- 2.47.3