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authorHerbert Xu <herbert@gondor.apana.org.au>2008-03-22 18:47:05 -0400
committerDavid S. Miller <davem@davemloft.net>2008-03-22 18:47:05 -0400
commit69d1506731168d6845a76a303b2c45f7c05f3f2c (patch)
tree3bedf2680b30c09b0375616a1c2b0d291a9f376f /net/ipv4
parent7512cbf6efc97644812f137527a54b8e92b6a90a (diff)
[TCP]: Let skbs grow over a page on fast peers
While testing the virtio-net driver on KVM with TSO I noticed that TSO performance with a 1500 MTU is significantly worse compared to the performance of non-TSO with a 16436 MTU. The packet dump shows that most of the packets sent are smaller than a page. Looking at the code this actually is quite obvious as it always stop extending the packet if it's the first packet yet to be sent and if it's larger than the MSS. Since each extension is bound by the page size, this means that (given a 1500 MTU) we're very unlikely to construct packets greater than a page, provided that the receiver and the path is fast enough so that packets can always be sent immediately. The fix is also quite obvious. The push calls inside the loop is just an optimisation so that we don't end up doing all the sending at the end of the loop. Therefore there is no specific reason why it has to do so at MSS boundaries. For TSO, the most natural extension of this optimisation is to do the pushing once the skb exceeds the TSO size goal. This is what the patch does and testing with KVM shows that the TSO performance with a 1500 MTU easily surpasses that of a 16436 MTU and indeed the packet sizes sent are generally larger than 16436. I don't see any obvious downsides for slower peers or connections, but it would be prudent to test this extensively to ensure that those cases don't regress. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/tcp.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 071e83a894ad..39b629ac2404 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -735,7 +735,7 @@ new_segment:
735 if (!(psize -= copy)) 735 if (!(psize -= copy))
736 goto out; 736 goto out;
737 737
738 if (skb->len < mss_now || (flags & MSG_OOB)) 738 if (skb->len < size_goal || (flags & MSG_OOB))
739 continue; 739 continue;
740 740
741 if (forced_push(tp)) { 741 if (forced_push(tp)) {
@@ -981,7 +981,7 @@ new_segment:
981 if ((seglen -= copy) == 0 && iovlen == 0) 981 if ((seglen -= copy) == 0 && iovlen == 0)
982 goto out; 982 goto out;
983 983
984 if (skb->len < mss_now || (flags & MSG_OOB)) 984 if (skb->len < size_goal || (flags & MSG_OOB))
985 continue; 985 continue;
986 986
987 if (forced_push(tp)) { 987 if (forced_push(tp)) {