netdev - Re: [PATCH net-next 07/10] net: group sk_backlog and sk_receive

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <willemdebruijn.kernel.a51d1cd6f43c@gmail.com>
Date: Wed, 17 Sep 2025 11:01:44 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Eric Dumazet <edumazet@...gle.com>, 
 "David S . Miller" <davem@...emloft.net>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, 
 Willem de Bruijn <willemb@...gle.com>, 
 Kuniyuki Iwashima <kuniyu@...gle.com>, 
 David Ahern <dsahern@...nel.org>, 
 netdev@...r.kernel.org, 
 eric.dumazet@...il.com, 
 Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 07/10] net: group sk_backlog and sk_receive_queue

Eric Dumazet wrote:
> 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 <edumazet@...gle.com>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>