diff options
author | Eric Dumazet <edumazet@google.com> | 2018-03-31 12:58:58 -0700 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2018-03-31 23:25:40 -0400 |
commit | bf66337140c64c27fa37222b7abca7e49d63fb57 (patch) | |
tree | 21a458948982fa21406bf356534516789d435661 /net/ipv4 | |
parent | c2615cf5a761b32bf74e85bddc223dfff3d9b9f0 (diff) | |
download | linux-bf66337140c64c27fa37222b7abca7e49d63fb57.tar.bz2 |
inet: frags: get rid of ipfrag_skb_cb/FRAG_CB
ip_defrag uses skb->cb[] to store the fragment offset, and unfortunately
this integer is currently in a different cache line than skb->next,
meaning that we use two cache lines per skb when finding the insertion point.
By aliasing skb->ip_defrag_offset and skb->dev, we pack all the fields
in a single cache line and save precious memory bandwidth.
Note that after the fast path added by Changli Gao in commit
d6bebca92c66 ("fragment: add fast path for in-order fragments")
this change wont help the fast path, since we still need
to access prev->len (2nd cache line), but will show great
benefits when slow path is entered, since we perform
a linear scan of a potentially long list.
Also, note that this potential long list is an attack vector,
we might consider also using an rb-tree there eventually.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
-rw-r--r-- | net/ipv4/ip_fragment.c | 35 |
1 files changed, 14 insertions, 21 deletions
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index fb185d9a5cc7..994fa70a910f 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -57,14 +57,6 @@ */ static const char ip_frag_cache_name[] = "ip4-frags"; -struct ipfrag_skb_cb -{ - struct inet_skb_parm h; - int offset; -}; - -#define FRAG_CB(skb) ((struct ipfrag_skb_cb *)((skb)->cb)) - /* Describe an entry in the "incomplete datagrams" queue. */ struct ipq { struct inet_frag_queue q; @@ -353,13 +345,13 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) * this fragment, right? */ prev = qp->q.fragments_tail; - if (!prev || FRAG_CB(prev)->offset < offset) { + if (!prev || prev->ip_defrag_offset < offset) { next = NULL; goto found; } prev = NULL; for (next = qp->q.fragments; next != NULL; next = next->next) { - if (FRAG_CB(next)->offset >= offset) + if (next->ip_defrag_offset >= offset) break; /* bingo! */ prev = next; } @@ -370,7 +362,7 @@ found: * any overlaps are eliminated. */ if (prev) { - int i = (FRAG_CB(prev)->offset + prev->len) - offset; + int i = (prev->ip_defrag_offset + prev->len) - offset; if (i > 0) { offset += i; @@ -387,8 +379,8 @@ found: err = -ENOMEM; - while (next && FRAG_CB(next)->offset < end) { - int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */ + while (next && next->ip_defrag_offset < end) { + int i = end - next->ip_defrag_offset; /* overlap is 'i' bytes */ if (i < next->len) { /* Eat head of the next overlapped fragment @@ -396,7 +388,7 @@ found: */ if (!pskb_pull(next, i)) goto err; - FRAG_CB(next)->offset += i; + next->ip_defrag_offset += i; qp->q.meat -= i; if (next->ip_summed != CHECKSUM_UNNECESSARY) next->ip_summed = CHECKSUM_NONE; @@ -420,7 +412,13 @@ found: } } - FRAG_CB(skb)->offset = offset; + /* Note : skb->ip_defrag_offset and skb->dev share the same location */ + dev = skb->dev; + if (dev) + qp->iif = dev->ifindex; + /* Makes sure compiler wont do silly aliasing games */ + barrier(); + skb->ip_defrag_offset = offset; /* Insert this fragment in the chain of fragments. */ skb->next = next; @@ -431,11 +429,6 @@ found: else qp->q.fragments = skb; - dev = skb->dev; - if (dev) { - qp->iif = dev->ifindex; - skb->dev = NULL; - } qp->q.stamp = skb->tstamp; qp->q.meat += skb->len; qp->ecn |= ecn; @@ -511,7 +504,7 @@ static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev, } WARN_ON(!head); - WARN_ON(FRAG_CB(head)->offset != 0); + WARN_ON(head->ip_defrag_offset != 0); /* Allocate a new buffer for the datagram. */ ihlen = ip_hdrlen(head); |