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authorXiaoliang (David) Wei <davidwei79@gmail.com>2006-07-11 13:03:28 -0700
committerDavid S. Miller <davem@sunset.davemloft.net>2006-07-12 13:58:50 -0700
commit6150c22e2ac3f7dbe73e7ae7817785070d0cff1f (patch)
tree2506ea47e5ae101ab6f0df694480b1df46267b18
parent781b456a980ec987a4be248f236c59658f651240 (diff)
[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>
-rw-r--r--net/ipv4/tcp_highspeed.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/net/ipv4/tcp_highspeed.c b/net/ipv4/tcp_highspeed.c
index aaa1538c069..fa3e1aad660 100644
--- a/net/ipv4/tcp_highspeed.c
+++ b/net/ipv4/tcp_highspeed.c
@@ -139,14 +139,19 @@ static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 rtt,
tp->snd_cwnd++;
}
} else {
- /* Update AIMD parameters */
+ /* Update AIMD parameters.
+ *
+ * We want to guarantee that:
+ * hstcp_aimd_vals[ca->ai-1].cwnd <
+ * snd_cwnd <=
+ * hstcp_aimd_vals[ca->ai].cwnd
+ */
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)
+ } else if (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd) {
+ while (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd)
ca->ai--;
}