[PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[Angelo P. Castellani]

From: Angelo P. Castellani <angelo.castellani@gmail.con>

RFC3742: limited slow start

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

Signed-off-by: Angelo P. Castellani <angelo.castellani@gmail.con>
---

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(+)

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[Angelo P. Castellani]

[-- Attachment #1: Type: text/plain, Size: 1012 bytes --]

Forgot the patch..

Angelo P. Castellani ha scritto:
> From: Angelo P. Castellani <angelo.castellani@gmail.con>
>
> RFC3742: limited slow start
>
> See http://www.ietf.org/rfc/rfc3742.txt
>
> Signed-off-by: Angelo P. Castellani <angelo.castellani@gmail.con>
> ---
>
> 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(+)
>
>


[-- Attachment #2: tcp_yeah-2of2.diff --]
[-- Type: text/x-patch, Size: 1662 bytes --]

diff -uprN linux-2.6.20-a/include/net/tcp.h linux-2.6.20-c/include/net/tcp.h
--- linux-2.6.20-a/include/net/tcp.h	2007-02-04 19:44:54.000000000 +0100
+++ linux-2.6.20-c/include/net/tcp.h	2007-02-19 10:54:10.000000000 +0100
@@ -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
--- linux-2.6.20-a/net/ipv4/tcp_cong.c	2007-02-04 19:44:54.000000000 +0100
+++ linux-2.6.20-c/net/ipv4/tcp_cong.c	2007-02-19 10:54:10.000000000 +0100
@@ -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;
+		}
+	} 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.

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[John Heffner]

[-- Attachment #1: Type: text/plain, Size: 3382 bytes --]

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.

Thanks,
   -John


Angelo P. Castellani wrote:
> Forgot the patch..
> 
> Angelo P. Castellani ha scritto:
>> From: Angelo P. Castellani <angelo.castellani@gmail.con>
>>
>> RFC3742: limited slow start
>>
>> See http://www.ietf.org/rfc/rfc3742.txt
>>
>> Signed-off-by: Angelo P. Castellani <angelo.castellani@gmail.con>
>> ---
>>
>> 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(+)
>>
>>
> 
> 
> ------------------------------------------------------------------------
> 
> diff -uprN linux-2.6.20-a/include/net/tcp.h linux-2.6.20-c/include/net/tcp.h
> --- linux-2.6.20-a/include/net/tcp.h	2007-02-04 19:44:54.000000000 +0100
> +++ linux-2.6.20-c/include/net/tcp.h	2007-02-19 10:54:10.000000000 +0100
> @@ -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
> --- linux-2.6.20-a/net/ipv4/tcp_cong.c	2007-02-04 19:44:54.000000000 +0100
> +++ linux-2.6.20-c/net/ipv4/tcp_cong.c	2007-02-19 10:54:10.000000000 +0100
> @@ -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;
> +		}
> +	} 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.


[-- Attachment #2: lss.patch --]
[-- Type: text/plain, Size: 3589 bytes --]

Add RFC3742 Limited Slow-Start, controlled by variable sysctl_tcp_max_ssthresh.

Signed-off-by: John Heffner <jheffner@psc.edu>

---
commit 97033fa201705e6cfc68ce66f34ede3277c3d645
tree 5df4607728abce93aa05b31015a90f2ce369abff
parent 8a03d9a498eaf02c8a118752050a5154852c13bf
author John Heffner <jheffner@psc.edu> Mon, 19 Feb 2007 15:52:16 -0500
committer John Heffner <jheffner@psc.edu> Mon, 19 Feb 2007 15:52:16 -0500

 include/linux/sysctl.h     |    1 +
 include/net/tcp.h          |    1 +
 net/ipv4/sysctl_net_ipv4.c |    8 ++++++++
 net/ipv4/tcp_cong.c        |   33 +++++++++++++++++++++++----------
 4 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 2c5fb38..a2dce72 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -438,6 +438,7 @@ enum
 	NET_CIPSOV4_RBM_STRICTVALID=121,
 	NET_TCP_AVAIL_CONG_CONTROL=122,
 	NET_TCP_ALLOWED_CONG_CONTROL=123,
+	NET_TCP_MAX_SSTHRESH=124,
 };
 
 enum {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5c472f2..521da28 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -230,6 +230,7 @@ extern int sysctl_tcp_mtu_probing;
 extern int sysctl_tcp_base_mss;
 extern int sysctl_tcp_workaround_signed_windows;
 extern int sysctl_tcp_slow_start_after_idle;
+extern int sysctl_tcp_max_ssthresh;
 
 extern atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 0aa3047..d68effe 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -803,6 +803,14 @@ #endif /* CONFIG_NETLABEL */
 		.proc_handler   = &proc_allowed_congestion_control,
 		.strategy	= &strategy_allowed_congestion_control,
 	},
+	{
+		.ctl_name	= NET_TCP_MAX_SSTHRESH,
+		.procname	= "tcp_max_ssthresh",
+		.data		= &sysctl_tcp_max_ssthresh,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 	{ .ctl_name = 0 }
 };
 
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index c1b34f1..7fd2910 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -12,6 +12,8 @@ #include <linux/types.h>
 #include <linux/list.h>
 #include <net/tcp.h>
 
+int sysctl_tcp_max_ssthresh = 0;
+
 static DEFINE_SPINLOCK(tcp_cong_list_lock);
 static LIST_HEAD(tcp_cong_list);
 
@@ -271,10 +273,13 @@ #endif
 
 
 /*
- * Linear increase during slow start
+ * Slow start (exponential increase) with
+ * RFC3742 Limited Slow Start (fast linear increase) support.
  */
 void tcp_slow_start(struct tcp_sock *tp)
 {
+	int cnt = 0;
+	
 	if (sysctl_tcp_abc) {
 		/* RFC3465: Slow Start
 		 * TCP sender SHOULD increase cwnd by the number of
@@ -283,17 +288,25 @@ void tcp_slow_start(struct tcp_sock *tp)
 		 */
 		if (tp->bytes_acked < tp->mss_cache)
 			return;
-
-		/* We MAY increase by 2 if discovered delayed ack */
-		if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache) {
-			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-				tp->snd_cwnd++;
-		}
 	}
+	
+	if (sysctl_tcp_max_ssthresh > 0 &&
+	    tp->snd_cwnd > sysctl_tcp_max_ssthresh)
+		cnt += sysctl_tcp_max_ssthresh>>1;
+	else
+		cnt += tp->snd_cwnd;
+
+	/* RFC3465: We MAY increase by 2 if discovered delayed ack */
+	if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
+		cnt <<= 1;
 	tp->bytes_acked = 0;
-
-	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-		tp->snd_cwnd++;
+	
+	tp->snd_cwnd_cnt += cnt;
+	while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+			tp->snd_cwnd++;
+		tp->snd_cwnd_cnt -= tp->snd_cwnd;
+	}
 }
 EXPORT_SYMBOL_GPL(tcp_slow_start);
 

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[Angelo P. Castellani]

John Heffner ha scritto:
> 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.

However more testing is good and welcome.

Regards,
Angelo P. Castellani

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[John Heffner]

Angelo P. Castellani wrote:
> John Heffner ha scritto:
>> 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.

Thanks,
   -John

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[Angelo P. Castellani]

John Heffner ha scritto:
> Sorry for the confusion.  The patch I attached to my message was 
> compile-tested only.
Well I've read your reply by night and I haven't seen that you attached 
a patch. Sorry for that.

Kind regards,
Angelo

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[David Miller]

From: "Angelo P. Castellani" <angelo.castellani@gmail.com>
Date: Mon, 19 Feb 2007 11:35:09 +0100

> From: Angelo P. Castellani <angelo.castellani@gmail.con>
> 
> RFC3742: limited slow start
> 
> See http://www.ietf.org/rfc/rfc3742.txt
> 
> Signed-off-by: Angelo P. Castellani <angelo.castellani@gmail.con>
> ---
> 
> 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.

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[David Miller]

From: John Heffner <jheffner@psc.edu>
Date: Mon, 19 Feb 2007 16:00:06 -0500

> 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?

When people post conflicting code bits for this for inclusion, it
makes work very difficult for me.

What I want to do right now is back everything out and let you guys
sort it out, but I don't want to do that because it would mean that
I just wasted an entire hour reviewing the YeaH patches. :-/

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[David Miller]

From: David Miller <davem@davemloft.net>
Date: Thu, 22 Feb 2007 00:27:04 -0800 (PST)

> 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:

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 2b4142b..5ee79f3 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -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.
diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c
index 2d971d1..815e020 100644
--- a/net/ipv4/tcp_yeah.c
+++ b/net/ipv4/tcp_yeah.c
@@ -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 */
 

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[John Heffner]

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.

Thanks,
   -John


David Miller wrote:
> From: David Miller <davem@davemloft.net>
> Date: Thu, 22 Feb 2007 00:27:04 -0800 (PST)
> 
>> 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:
> 
> diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> index 2b4142b..5ee79f3 100644
> --- a/net/ipv4/tcp_cong.c
> +++ b/net/ipv4/tcp_cong.c
> @@ -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.
> diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c
> index 2d971d1..815e020 100644
> --- a/net/ipv4/tcp_yeah.c
> +++ b/net/ipv4/tcp_yeah.c
> @@ -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 majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[David Miller]

From: John Heffner <jheffner@psc.edu>
Date: Thu, 22 Feb 2007 09:25:07 -0500

> 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.

I noticed that after sending out my diff and corrected it before
pushing to tcp-2.6, thanks :-)

Re: [PATCH 2/2][TCP] YeAH-TCP: limited slow start exported function

[Angelo P. Castellani]

Ok, I've missed this bit in the submitting patches documentation..
however sorry for that.

2007/2/22, David Miller <davem@davemloft.net>:
> 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.
>