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authorNeal Cardwell <ncardwell@google.com>2012-04-10 07:59:20 +0000
committerDavid S. Miller <davem@davemloft.net>2012-04-10 14:47:09 -0400
commit18a223e0b9ec8979320ba364b47c9772391d6d05 (patch)
tree0028fe1163490ced0dcf3d72384fba0e37cf085e
parent5fb84b1428b271f8767e0eb3fcd7231896edfaa4 (diff)
tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample
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>
-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 e886e2f7fa8d..e7b54d29690e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -474,8 +474,11 @@ 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;