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authorNeal Cardwell <ncardwell@google.com>2012-04-10 07:59:20 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-04-27 09:51:19 -0700
commit4a1abcbd24d856fe49029c3dc6f7fe8dc66ddaac (patch)
tree12b1633d5ff3cbcf76e3e4d89202250823406abe
parent6d7946bd33e29b2659504ffb3b98aa9fdb2229d8 (diff)
tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample
[ Upstream commit 18a223e0b9ec8979320ba364b47c9772391d6d05 ] Fix a code path in tcp_rcv_rtt_update() that was comparing scaled and unscaled RTT samples. The intent in the code was to only use the 'm' measurement if it was a new minimum. However, since 'm' had not yet been shifted left 3 bits but 'new_sample' had, this comparison would nearly always succeed, leading us to erroneously set our receive-side RTT estimate to the 'm' sample when that sample could be nearly 8x too high to use. The overall effect is to often cause the receive-side RTT estimate to be significantly too large (up to 40% too large for brief periods in my tests). Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--net/ipv4/tcp_input.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 72b1857723da..104b02e3ee2a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -460,8 +460,11 @@ static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
if (!win_dep) {
m -= (new_sample >> 3);
new_sample += m;
- } else if (m < new_sample)
- new_sample = m << 3;
+ } else {
+ m <<= 3;
+ if (m < new_sample)
+ new_sample = m;
+ }
} else {
/* No previous measure. */
new_sample = m << 3;