Message ID | 1459377448-2239-4-git-send-email-soheil.kdev@gmail.com |
---|---|
State | Changes Requested, archived |
Delegated to: | David Miller |
Headers | show |
On Wed, Mar 30, 2016 at 6:37 PM, Soheil Hassas Yeganeh <soheil.kdev@gmail.com> wrote: > From: Soheil Hassas Yeganeh <soheil@google.com> > > Currently, to avoid a cache line miss for accessing skb_shinfo, > tcp_ack_tstamp skips socket that do not have > SOF_TIMESTAMPING_TX_ACK bit set in sk_tsflags. This is > implemented based on an implicit assumption that the > SOF_TIMESTAMPING_TX_ACK is set via socket options for the > duration that ACK timestamps are needed. > > To implement per-write timestamps, this check should be > removed and replaced with a per-packet alternative that > quickly skips packets missing ACK timestamps marks without > a cache-line miss. > > To enable per-packet marking without a cache line miss, use > one bit in TCP_SKB_CB to mark a whether a SKB might need a > ack tx timestamp or not. Further checks in tcp_ack_tstamp are not > modified and work as before. > > Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Acked-by: Willem de Bruijn <willemb@google.com>
diff --git a/include/net/tcp.h b/include/net/tcp.h index b91370f..f3a80ec 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -754,7 +754,8 @@ struct tcp_skb_cb { TCPCB_REPAIRED) __u8 ip_dsfield; /* IPv4 tos or IPv6 dsfield */ - /* 1 byte hole */ + __u8 txstamp_ack:1, /* Record TX timestamp for ack? */ + unused:7; __u32 ack_seq; /* Sequence number ACK'd */ union { struct inet_skb_parm h4; diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 08b8b96..ce3c9eb 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -432,10 +432,12 @@ static void tcp_tx_timestamp(struct sock *sk, struct sk_buff *skb) { if (sk->sk_tsflags) { struct skb_shared_info *shinfo = skb_shinfo(skb); + struct tcp_skb_cb *tcb = TCP_SKB_CB(skb); sock_tx_timestamp(sk, &shinfo->tx_flags); if (shinfo->tx_flags & SKBTX_ANY_TSTAMP) shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1; + tcb->txstamp_ack = !!(shinfo->tx_flags & SKBTX_ACK_TSTAMP); } } diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index e6e65f7..2d5fee4 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3093,7 +3093,7 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb, const struct skb_shared_info *shinfo; /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */ - if (likely(!(sk->sk_tsflags & SOF_TIMESTAMPING_TX_ACK))) + if (likely(!TCP_SKB_CB(skb)->txstamp_ack)) return; shinfo = skb_shinfo(skb);