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authorEric Dumazet <edumazet@google.com>2014-09-27 09:50:57 -0700
committerDavid S. Miller <davem@davemloft.net>2014-09-28 16:35:43 -0400
commit971f10eca186cab238c49daa91f703c5a001b0b1 (patch)
tree0d769e6155899c89ae95c3e31c79ce011eb96a39 /net
parenta224772db8420ecb7ce91a9ba5d535ee3a50d982 (diff)
tcp: better TCP_SKB_CB layout to reduce cache line misses
TCP maintains lists of skb in write queue, and in receive queues (in order and out of order queues) Scanning these lists both in input and output path usually requires access to skb->next, TCP_SKB_CB(skb)->seq, and TCP_SKB_CB(skb)->end_seq These fields are currently in two different cache lines, meaning we waste lot of memory bandwidth when these queues are big and flows have either packet drops or packet reorders. We can move TCP_SKB_CB(skb)->header at the end of TCP_SKB_CB, because this header is not used in fast path. This allows TCP to search much faster in the skb lists. Even with regular flows, we save one cache line miss in fast path. Thanks to Christoph Paasch for noticing we need to cleanup skb->cb[] (IPCB/IP6CB) before entering IP stack in tx path, and that I forgot IPCB use in tcp_v4_hnd_req() and tcp_v4_save_options(). Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_ipv4.c19
-rw-r--r--net/ipv4/tcp_output.c5
-rw-r--r--net/ipv6/tcp_ipv6.c7
3 files changed, 24 insertions, 7 deletions
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 28ab90382c01..9ce3eac02957 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -886,18 +886,16 @@ EXPORT_SYMBOL(tcp_syn_flood_action);
*/
static struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
{
- const struct ip_options *opt = &(IPCB(skb)->opt);
+ const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
struct ip_options_rcu *dopt = NULL;
if (opt && opt->optlen) {
int opt_size = sizeof(*dopt) + opt->optlen;
dopt = kmalloc(opt_size, GFP_ATOMIC);
- if (dopt) {
- if (ip_options_echo(&dopt->opt, skb)) {
- kfree(dopt);
- dopt = NULL;
- }
+ if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
+ kfree(dopt);
+ dopt = NULL;
}
}
return dopt;
@@ -1431,7 +1429,7 @@ static struct sock *tcp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
#ifdef CONFIG_SYN_COOKIES
if (!th->syn)
- sk = cookie_v4_check(sk, skb, &(IPCB(skb)->opt));
+ sk = cookie_v4_check(sk, skb, &TCP_SKB_CB(skb)->header.h4.opt);
#endif
return sk;
}
@@ -1636,6 +1634,13 @@ int tcp_v4_rcv(struct sk_buff *skb)
th = tcp_hdr(skb);
iph = ip_hdr(skb);
+ /* This is tricky : We move IPCB at its correct location into TCP_SKB_CB()
+ * barrier() makes sure compiler wont play fool^Waliasing games.
+ */
+ memmove(&TCP_SKB_CB(skb)->header.h4, IPCB(skb),
+ sizeof(struct inet_skb_parm));
+ barrier();
+
TCP_SKB_CB(skb)->seq = ntohl(th->seq);
TCP_SKB_CB(skb)->end_seq = (TCP_SKB_CB(skb)->seq + th->syn + th->fin +
skb->len - th->doff * 4);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f173b1c4f815..a462fb1db896 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -974,6 +974,11 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
/* Our usage of tstamp should remain private */
skb->tstamp.tv64 = 0;
+
+ /* Cleanup our debris for IP stacks */
+ memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
+ sizeof(struct inet6_skb_parm)));
+
err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
if (likely(err <= 0))
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 9400b4326f22..132bac137aed 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1412,6 +1412,13 @@ static int tcp_v6_rcv(struct sk_buff *skb)
th = tcp_hdr(skb);
hdr = ipv6_hdr(skb);
+ /* This is tricky : We move IPCB at its correct location into TCP_SKB_CB()
+ * barrier() makes sure compiler wont play fool^Waliasing games.
+ */
+ memmove(&TCP_SKB_CB(skb)->header.h6, IP6CB(skb),
+ sizeof(struct inet6_skb_parm));
+ barrier();
+
TCP_SKB_CB(skb)->seq = ntohl(th->seq);
TCP_SKB_CB(skb)->end_seq = (TCP_SKB_CB(skb)->seq + th->syn + th->fin +
skb->len - th->doff*4);