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;