On Thu, 2017-03-30 at 14:03 +0200, Paolo Abeni wrote:
> sock_recv_ts_and_drops() unconditionally set sk->sk_stamp for
> every packet, even if the SOCK_TIMESTAMP flag is not set in the
> related socket.
> If selinux is enabled, this cause a cache miss for every packet
> since sk->sk_stamp and sk->sk_security share the same cacheline.
> With this change sk_stamp is set only if the SOCK_TIMESTAMP
> flag is set, and is cleared for the first packet, so that the user
> perceived behavior is unchanged.
>
> This gives up to 5% speed-up under udp-flood with small packets.
>
> Signed-off-by: Paolo Abeni <pab...@redhat.com>
> ---
> include/net/sock.h | 5 ++++-
> net/core/sock.c | 2 +-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index cb241a0..8e53158 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2239,6 +2239,7 @@ sock_recv_timestamp(struct msghdr *msg, struct sock
> *sk, struct sk_buff *skb)
> void __sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
> struct sk_buff *skb);
>
> +#define SK_DEFAULT_STAMP (-1L * NSEC_PER_SEC)
> static inline void sock_recv_ts_and_drops(struct msghdr *msg, struct sock
> *sk,
> struct sk_buff *skb)
> {
> @@ -2249,8 +2250,10 @@ static inline void sock_recv_ts_and_drops(struct
> msghdr *msg, struct sock *sk,
>
> if (sk->sk_flags & FLAGS_TS_OR_DROPS || sk->sk_tsflags & TSFLAGS_ANY)
> __sock_recv_ts_and_drops(msg, sk, skb);
> - else
> + else if (unlikely(sk->sk_flags & SOCK_TIMESTAMP))
> sk->sk_stamp = skb->tstamp;
> + else if (unlikely(sk->sk_stamp == SK_DEFAULT_STAMP))
> + sk->sk_stamp = 0;
> }
>
This looks very nice, but why using 0 here instead of skb->tstamp ?
This might give some regression on applications reading their first
socket timestamp in some contexts.
What about
if (sk->sk_flags & FLAGS_TS_OR_DROPS || sk->sk_tsflags & TSFLAGS_ANY)
__sock_recv_ts_and_drops(msg, sk, skb);
else if (unlikely(sk->sk_flags & SOCK_TIMESTAMP ||
sk->sk_stamp == SK_DEFAULT_STAMP))
sk->sk_stamp = skb->tstamp;
