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4effb335b5
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@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250916160951.541279-8-edumazet@google.com
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.