From: Xiaoliang (David) Wei <davidwei79@gmail.com>
Date: Tue, 11 Jul 2006 20:03:28 +0000 (-0700)
Subject: [TCP] tcp_highspeed: Fix AI updates.
X-Git-Tag: v2.6.18-rc2~93^2~12
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6150c22e2ac3f7dbe73e7ae7817785070d0cff1f;p=pandora-kernel.git

[TCP] tcp_highspeed: Fix AI updates.

I think there is still a problem with the AIMD parameter update in
HighSpeed TCP code.

Line 125~138 of the code (net/ipv4/tcp_highspeed.c):

	/* Update AIMD parameters */
	if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
		while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
		       ca->ai < HSTCP_AIMD_MAX - 1)
			ca->ai++;
	} else if (tp->snd_cwnd < hstcp_aimd_vals[ca->ai].cwnd) {
		while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
		       ca->ai > 0)
			ca->ai--;

In fact, the second part (decreasing ca->ai) never decreases since the
while loop's inequality is in the reverse direction. This leads to
unfairness with multiple flows (once a flow happens to enjoy a higher
ca->ai, it keeps enjoying that even its cwnd decreases)

Here is a tentative fix (I also added a comment, trying to keep the
change clear):

Acked-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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