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| author | Neal Cardwell <ncardwell@google.com> | 2012-04-10 07:59:20 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-04-27 10:17:04 -0700 |
| commit | 8607ccff19e16b51feab33664425e5984f751074 (patch) | |
| tree | fee8a4f7f0a2bb5e90907a306fe876dde6f4bdfb | |
| parent | ce30c9603e01ed68e7536a0936f30ec047acd57f (diff) | |
| download | linux-stable-8607ccff19e16b51feab33664425e5984f751074.tar.gz linux-stable-8607ccff19e16b51feab33664425e5984f751074.tar.bz2 linux-stable-8607ccff19e16b51feab33664425e5984f751074.zip | |
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.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index b5e315f13641..7b075dd822eb 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -472,8 +472,11 @@ 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; |