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authorHerbert Xu <herbert@gondor.apana.org.au>2008-04-06 23:43:38 -0700
committerChris Wright <chrisw@sous-sol.org>2008-04-18 18:53:26 -0700
commit276be82fbc8970d7dac375493d699f8bea015e7f (patch)
treef322ca7fddc42af7e7f2173696d8d0796b240bb7
parentaf5ee471275ea3b943b3aa98e675eeee062aa83c (diff)
TCP: Let skbs grow over a page on fast peers
Upstream commit: 69d1506731168d6845a76a303b2c45f7c05f3f2c 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> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
-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 8e65182f7af1..43051546deae 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -583,7 +583,7 @@ new_segment:
if (!(psize -= copy))
goto out;
- if (skb->len < mss_now || (flags & MSG_OOB))
+ if (skb->len < size_goal || (flags & MSG_OOB))
continue;
if (forced_push(tp)) {
@@ -829,7 +829,7 @@ new_segment:
if ((seglen -= copy) == 0 && iovlen == 0)
goto out;
- if (skb->len < mss_now || (flags & MSG_OOB))
+ if (skb->len < size_goal || (flags & MSG_OOB))
continue;
if (forced_push(tp)) {