From: Neal Cardwell Date: Tue, 10 Apr 2012 07:59:20 +0000 (+0000) Subject: tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample X-Git-Tag: v3.4~221^2~5 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=18a223e0b9ec8979320ba364b47c9772391d6d05;p=platform%2Fkernel%2Flinux-amlogic.git 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 Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index e886e2f..e7b54d2 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;