commit 18a223e0b9ec8979320ba364b47c9772391d6d05
author Neal Cardwell <ncardwell@google.com> Tue Apr 10 07:59:20 2012 +0000
committer David S. Miller <davem@davemloft.net> Tue Apr 10 14:47:09 2012 -0400
tree 0028fe1163490ced0dcf3d72384fba0e37cf085e
parent 5fb84b1428b271f8767e0eb3fcd7231896edfaa4

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>