GitHub-Mirror/linux-bl808
2
0
Fork 0
mirror of https://github.com/Fishwaldo/linux-bl808.git synced 2025-06-17 20:25:19 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

tcp: better TCP_SKB_CB layout to reduce cache line misses

Browse source 
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>
This commit is contained in:
Eric Dumazet 2014-09-27 09:50:57 -07:00 • committed by David S. Miller
parent a224772db8
commit 971f10eca1
4 changed files with 30 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

7
net/ipv6/tcp_ipv6.c
View file

@ -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);