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authorAlexey Kuznetsov <kuznet@ms2.inr.ac.ru>2010-09-15 10:27:52 -0700
committerDavid S. Miller <davem@davemloft.net>2010-09-15 12:01:44 -0700
commit01f83d69844d307be2aa6fea88b0e8fe5cbdb2f4 (patch)
treeb01eba7a8b9cf737312c3721ff8ef361baa55bea
parent6dcbc12290abb452a5e42713faa6461b248e2f55 (diff)
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tcp: Prevent overzealous packetization by SWS logic.
If peer uses tiny MSS (say, 75 bytes) and similarly tiny advertised window, the SWS logic will packetize to half the MSS unnecessarily. This causes problems with some embedded devices. However for large MSS devices we do want to half-MSS packetize otherwise we never get enough packets into the pipe for things like fast retransmit and recovery to work. Be careful also to handle the case where MSS > window, otherwise we'll never send until the probe timer. Reported-by: ツ Leandro Melo de Sales <leandroal@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/tcp.h18
1 files changed, 16 insertions, 2 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index eaa9582779d..3e4b33e3660 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -475,8 +475,22 @@ extern unsigned int tcp_current_mss(struct sock *sk);
/* Bound MSS / TSO packet size with the half of the window */
static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
{
- if (tp->max_window && pktsize > (tp->max_window >> 1))
- return max(tp->max_window >> 1, 68U - tp->tcp_header_len);
+ int cutoff;
+
+ /* When peer uses tiny windows, there is no use in packetizing
+ * to sub-MSS pieces for the sake of SWS or making sure there
+ * are enough packets in the pipe for fast recovery.
+ *
+ * On the other hand, for extremely large MSS devices, handling
+ * smaller than MSS windows in this way does make sense.
+ */
+ if (tp->max_window >= 512)
+ cutoff = (tp->max_window >> 1);
+ else
+ cutoff = tp->max_window;
+
+ if (cutoff && pktsize > cutoff)
+ return max_t(int, cutoff, 68U - tp->tcp_header_len);
else
return pktsize;
}