On Fri, 2017-03-31 at 11:47 +0200, Paolo Abeni wrote:
> In the udp_sock struct, the 'forward_deficit' and 'pcflag' fields
> share the same cacheline. While the first is dirtied by
> udp_recvmsg, the latter is read, possibly several times, by the
> bottom half processing to discriminate between udp and udplite
> sockets.
>
> With this patch, sk->sk_protocol is used to check is the socket is
> really an udplite one, avoiding some cache misses per
> packet and improving the performance under udp_flood with
> small packet up to 10%.
>
> Signed-off-by: Paolo Abeni <pab...@redhat.com>
> ---
> include/linux/udp.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/udp.h b/include/linux/udp.h
> index c0f5308..6cb4061 100644
> --- a/include/linux/udp.h
> +++ b/include/linux/udp.h
> @@ -115,6 +115,6 @@ static inline bool udp_get_no_check6_rx(struct sock *sk)
> #define udp_portaddr_for_each_entry_rcu(__sk, list) \
> hlist_for_each_entry_rcu(__sk, list, __sk_common.skc_portaddr_node)
>
> -#define IS_UDPLITE(__sk) (udp_sk(__sk)->pcflag)
> +#define IS_UDPLITE(__sk) (__sk->sk_protocol == IPPROTO_UDPLITE)
>
> #endif /* _LINUX_UDP_H */
I am pretty sure we agreed in the past that forward_deficit would need
to be placed on a cache line of its own. Somehow we manage to not
implement this properly.
What about other fields like encap_rcv, encap_destroy, gro_receive,
gro_complete. They really should have the same false sharing issue.
Proper fix is :
include/linux/udp.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/include/linux/udp.h b/include/linux/udp.h
index
c0f530809d1f3db7323e51a52224eb49d8f97da0..bdfd11823c12f6c08dc6b2adb247b8e0a7f2e5d5
100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -80,8 +80,10 @@ struct udp_sock {
struct sk_buff *skb,
int nhoff);
- /* This field is dirtied by udp_recvmsg() */
- int forward_deficit;
+ /* This field is dirtied by udp_recvmsg().
+ * Make sure it wont share a cache line with prior fields.
+ */
+ int forward_deficit ____cacheline_aligned_in_smp;
};
static inline struct udp_sock *udp_sk(const struct sock *sk)
