YeAH-TCP: limited slow start exported function

From: Angelo P. Castellani <[email protected]>

RFC3742: limited slow start

See http://www.ietf.org/rfc/rfc3742.txt

Signed-off-by Angelo P. Castellani <[email protected]>

---

To allow code reutilization I've added the limited slow start procedure as an exported symbol of linux tcp congestion control.

On large BDP networks canonical slow start should be avoided because it requires large packet losses to converge, whereas at lower BDPs slow start and limited slow start are identical. Large BDP is defined through the max_ssthresh variable.

I think limited slow start could safely replace the canonical slow start procedure in Linux.

Regards,
Angelo P. Castellani

p.s.: in the attached patch is added an exported function currently used only by YeAH TCP

include/net/tcp.h | 1 +
net/ipv4/tcp_cong.c | 23 +++++++++++++++++++++++

2 files changed, 24 insertions(+)

Forgot the patch..

Angelo P. Castellani ha scritto:

Quoted 15 lines

From: Angelo P. Castellani <[email protected]>

RFC3742: limited slow start

See http://www.ietf.org/rfc/rfc3742.txt

Signed-off-by Angelo P. Castellani <[email protected]>

---

To allow code reutilization I've added the limited slow start procedure as an exported symbol of linux tcp congestion control.

On large BDP networks canonical slow start should be avoided because it requires large packet losses to converge, whereas at lower BDPs slow start and limited slow start are identical. Large BDP is defined through the max_ssthresh variable.

I think limited slow start could safely replace the canonical slow start procedure in Linux.

Quoted 10 lines

Regards,
Angelo P. Castellani

p.s.: in the attached patch is added an exported function currently used only by YeAH TCP

include/net/tcp.h | 1 +
net/ipv4/tcp_cong.c | 23 +++++++++++++++++++++++

2 files changed, 24 insertions(+)

------------------------------------------------------------------------

diff -uprN linux-2.6.20-a/include/net/tcp.h linux-2.6.20-c/include/net/tcp.h

include/net/tcp.h +1 -0

@@ -669,6 +669,7 @@ extern void tcp_get_allowed_congestion_c
 extern int tcp_set_allowed_congestion_control(char *allowed);
 extern int tcp_set_congestion_control(struct sock *sk, const char *name);
 extern void tcp_slow_start(struct tcp_sock *tp);
+extern void tcp_limited_slow_start(struct tcp_sock *tp);
 
 extern struct tcp_congestion_ops tcp_init_congestion_ops;
 extern u32 tcp_reno_ssthresh(struct sock *sk);

diff -uprN linux-2.6.20-a/net/ipv4/tcp_cong.c linux-2.6.20-c/net/ipv4/tcp_cong.c

net/ipv4/tcp_cong.c +16 -0

@@ -297,6 +297,29 @@ void tcp_slow_start(struct tcp_sock *tp)
 }
 EXPORT_SYMBOL_GPL(tcp_slow_start);
 
+void tcp_limited_slow_start(struct tcp_sock *tp)
+{
+	/* RFC3742: limited slow start
+	 * the window is increased by 1/K MSS for each arriving ACK,
+	 * for K = int(cwnd/(0.5 max_ssthresh))
+	 */
+
+	const int max_ssthresh = 100;
+
+	if (max_ssthresh > 0 && tp->snd_cwnd > max_ssthresh) {
+		u32 k = max(tp->snd_cwnd / (max_ssthresh >> 1), 1U);
+		if (++tp->snd_cwnd_cnt >= k) {
+			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+				tp->snd_cwnd++;
+			tp->snd_cwnd_cnt = 0;
+		}

Note the patch is compile-tested only! I can do some real testing if you'd like to apply this Dave.

John Heffner ha scritto:

Quoted 1 line

Note the patch is compile-tested only! I can do some real testing if you'd like to apply this Dave.

The date you read on the patch is due to the fact I've splitted this patchset into 2 diff files. This isn't compile-tested only, I've used this piece of code for about 3 months.

Sorry for the confusion. The patch I attached to my message was compile-tested only.

I'd prefer to make it apply automatically across all congestion controls that do slow-start, and also make the max_ssthresh parameter controllable via sysctl. This patch (attached) should implement this. Note the default value for sysctl_tcp_max_ssthresh = 0, which disables limited slow-start. This should make ABC apply during LSS as well.

Note the patch is compile-tested only! I can do some real testing if you'd like to apply this Dave.

I'll apply this, but could you please also when making suggestions like this provide the patch necessary to kill the function added for YeaH and the call site in the YeaH algorithm?

From: David Miller <[email protected]>
Date: Thu, 22 Feb 2007 00:27:04 -0800 (PST)

Quoted 3 lines

I'll apply this, but could you please also when making suggestions like this provide the patch necessary to kill the function added for YeaH and the call site in the YeaH algorithm?

Here is how I'm resolving this:

net/ipv4/tcp_cong.c +0 -23

index 2b4142b..5ee79f3 100644
@@ -310,29 +310,6 @@ void tcp_slow_start(struct tcp_sock *tp)
 }
 EXPORT_SYMBOL_GPL(tcp_slow_start);
 
-void tcp_limited_slow_start(struct tcp_sock *tp)
-{
-	/* RFC3742: limited slow start
-	 * the window is increased by 1/K MSS for each arriving ACK,
-	 * for K = int(cwnd/(0.5 max_ssthresh))
-	 */
-
-	const int max_ssthresh = 100;
-
-	if (max_ssthresh > 0 && tp->snd_cwnd > max_ssthresh) {
-		u32 k = max(tp->snd_cwnd / (max_ssthresh >> 1), 1U);
-		if (++tp->snd_cwnd_cnt >= k) {
-			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-				tp->snd_cwnd++;
-			tp->snd_cwnd_cnt = 0;
-		}
-	} else {
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-			tp->snd_cwnd++;
-	}
-}
-EXPORT_SYMBOL_GPL(tcp_limited_slow_start);
-
 /*
  * TCP Reno congestion control
  * This is special case used for fallback as well.

net/ipv4/tcp_yeah.c +1 -2

index 2d971d1..815e020 100644
@@ -104,7 +104,7 @@ static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack,
 		return;
 
 	if (tp->snd_cwnd <= tp->snd_ssthresh) {
-		tcp_limited_slow_start(tp);
+		tcp_slow_start(tp);
 	} else if (!yeah->doing_reno_now) {
 		/* Scalable */
 
-

To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

My patch is meant as a replacement for YeAH patch 2/2, not meant to back it out. You do still need the second hunk below. Sorry 'bout that.

If you're going to apply YeAH patch 2/2 first, you will also need to remove the declaration of tcp_limited_slow_start() in include/net/tcp.h.

From: Angelo P. Castellani <[email protected]>

RFC3742: limited slow start

See http://www.ietf.org/rfc/rfc3742.txt

Signed-off-by Angelo P. Castellani <[email protected]>

---

To allow code reutilization I've added the limited slow start procedure as an exported symbol of linux tcp congestion control.

On large BDP networks canonical slow start should be avoided because it requires large packet losses to converge, whereas at lower BDPs slow start and limited slow start are identical. Large BDP is defined through the max_ssthresh variable.

I think limited slow start could safely replace the canonical slow start procedure in Linux.

p.s.: in the attached patch is added an exported function currently used only by YeAH TCP

Please never submit patches like this, submit the infrastructure FIRST, then submit the stuff that uses it. When a sequence of patches is applied, in sequence, the tree should build properly (even with all available new options enabled) at each step along the way.

Otherwise we have the situation we have now, in that YeaH is in my tree but doesn't build successfully.

What I'm going to do to "fix" this, is yank YeaH implementation out of my tree, add this second patch first, then add the YeaH patch back.

Please never do this again.