[RFC]: tfrc_tx_hist_rtt

[RFC]: tfrc_tx_hist_rtt

[Arnaldo Carvalho de Melo]

Hi Gerrit,

	Coming back to hiding the TX history data structures, take a
look at what I'm commiting to my tree:

1. struct tfrc_tx_hist_entry is completely hidden in
   net/dccp/ccids/lib/packet_history.c
2. I found tfrc_tx_hist_when confusing and returning two results, if it
   had found the ackno in the history and the timestamp, so I introduced
   tfrc_tx_hist_rtt instead, that returns 0 if the ackno was not found.

Does this looks reasonable?

- Arnaldo

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 2668de8..5dea690 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -399,7 +399,6 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
 	struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
 	struct ccid3_options_received *opt_recv;
-	struct tfrc_tx_hist_entry *packet;
 	ktime_t now;
 	unsigned long t_nfb;
 	u32 pinv, r_sample;
@@ -414,19 +413,17 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 	switch (hctx->ccid3hctx_state) {
 	case TFRC_SSTATE_NO_FBACK:
 	case TFRC_SSTATE_FBACK:
+		now = ktime_get_real();
+
 		/* estimate RTT from history if ACK number is valid */
-		packet = tfrc_tx_hist_find_entry(hctx->ccid3hctx_hist,
-						 DCCP_SKB_CB(skb)->dccpd_ack_seq);
-		if (packet = NULL) {
+		r_sample = tfrc_tx_hist_rtt(hctx->ccid3hctx_hist,
+					    DCCP_SKB_CB(skb)->dccpd_ack_seq, now);
+		if (r_sample = 0) {
 			DCCP_WARN("%s(%p): %s with bogus ACK-%llu\n", dccp_role(sk), sk,
 				  dccp_packet_name(DCCP_SKB_CB(skb)->dccpd_type),
 				  (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq);
 			return;
 		}
-		/*
-		 * Garbage-collect older (irrelevant) entries
-		 */
-		tfrc_tx_hist_purge(&packet->next);
 
 		/* Update receive rate in units of 64 * bytes/second */
 		hctx->ccid3hctx_x_recv = opt_recv->ccid3or_receive_rate;
@@ -438,12 +435,10 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 			hctx->ccid3hctx_p = 0;
 		else				       /* can not exceed 100% */
 			hctx->ccid3hctx_p = 1000000 / pinv;
-
-		now = ktime_get_real();
 		/*
-		 * Calculate new RTT sample and update moving average
+		 * Validate new RTT sample and update moving average
 		 */
-		r_sample = dccp_sample_rtt(sk, ktime_us_delta(now, packet->stamp));
+		r_sample = dccp_sample_rtt(sk, r_sample);
 		hctx->ccid3hctx_rtt = tfrc_ewma(hctx->ccid3hctx_rtt, r_sample, 9);
 
 		if (hctx->ccid3hctx_state = TFRC_SSTATE_NO_FBACK) {
diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
index 1397360..4805de9 100644
--- a/net/dccp/ccids/lib/packet_history.c
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -39,12 +39,24 @@
 #include <linux/string.h>
 #include "packet_history.h"
 
+/**
+ *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
+ *  @next:  next oldest entry (LIFO order)
+ *  @seqno: sequence number of this entry
+ *  @stamp: send time of packet with sequence number @seqno
+ */
+struct tfrc_tx_hist_entry {
+	struct tfrc_tx_hist_entry *next;
+	u64			  seqno;
+	ktime_t			  stamp;
+};
+
 /*
  * Transmitter History Routines
  */
 static struct kmem_cache *tfrc_tx_hist;
 
-struct tfrc_tx_hist_entry *
+static struct tfrc_tx_hist_entry *
 	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
 {
 	while (head != NULL && head->seqno != seqno)
@@ -52,7 +64,6 @@ struct tfrc_tx_hist_entry *
 
 	return head;
 }
-EXPORT_SYMBOL_GPL(tfrc_tx_hist_find_entry);
 
 int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno)
 {
@@ -83,6 +94,24 @@ void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)
 }
 EXPORT_SYMBOL_GPL(tfrc_tx_hist_purge);
 
+u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno,
+		     const ktime_t now)
+{
+	u32 rtt = 0;
+	struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);
+
+	if (packet != NULL) {
+		rtt = ktime_us_delta(now, packet->stamp);
+		/*
+		 * Garbage-collect older (irrelevant) entries:
+		 */
+		tfrc_tx_hist_purge(&packet->next);
+	}
+
+	return rtt;
+}
+EXPORT_SYMBOL_GPL(tfrc_tx_hist_rtt);
+
 /*
  * 	Receiver History Routines
  */
diff --git a/net/dccp/ccids/lib/packet_history.h b/net/dccp/ccids/lib/packet_history.h
index 5c07182..0670f46 100644
--- a/net/dccp/ccids/lib/packet_history.h
+++ b/net/dccp/ccids/lib/packet_history.h
@@ -48,23 +48,12 @@
 #define TFRC_WIN_COUNT_PER_RTT	 4
 #define TFRC_WIN_COUNT_LIMIT	16
 
-/**
- *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
- *  @next:  next oldest entry (LIFO order)
- *  @seqno: sequence number of this entry
- *  @stamp: send time of packet with sequence number @seqno
- */
-struct tfrc_tx_hist_entry {
-	struct tfrc_tx_hist_entry *next;
-	u64			  seqno;
-	ktime_t			  stamp;
-};
+struct tfrc_tx_hist_entry;
 
 extern int  tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno);
 extern void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp);
-
-extern struct tfrc_tx_hist_entry *
-	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 ackno);
+extern u32  tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head,
+			     const u64 seqno, const ktime_t now);
 
 /*
  * 	Receiver History data structures and declarations

Re: [RFC]: tfrc_tx_hist_rtt

[Gerrit Renker]

Sorry I only got this email today and it is a busy day, too.

The changes look good and are in general a further improvement on the
code. I like the idea of hiding the internals of the list structure in 
the source file.

I wonder if one could go one step further and also take the timestamp
directly when looking up the previous history sample, e.g.

	u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno)
	{
		u32 rtt = 0;
		struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);
	
		if (packet != NULL) {
			rtt = ktime_us_delta(ktime_get_real(), packet->stamp);
			/*
			 * Garbage-collect older (irrelevant) entries:
			 */
			tfrc_tx_hist_purge(&packet->next);
		}
	
		return rtt;
	}

Just a suggestion.

Thanks for looking through this.

Re: [RFC]: tfrc_tx_hist_rtt

[Arnaldo Carvalho de Melo]

Em Fri, Nov 30, 2007 at 12:19:36PM +0000, Gerrit Renker escreveu:
> Sorry I only got this email today and it is a busy day, too.
> 
> The changes look good and are in general a further improvement on the
> code. I like the idea of hiding the internals of the list structure in 
> the source file.
> 
> I wonder if one could go one step further and also take the timestamp
> directly when looking up the previous history sample, e.g.
> 
> 	u32 tfrc_tx_hist_rtt(struct tfrc_tx_hist_entry *head, const u64 seqno)
> 	{
> 		u32 rtt = 0;
> 		struct tfrc_tx_hist_entry *packet = tfrc_tx_hist_find_entry(head, seqno);
> 	
> 		if (packet != NULL) {
> 			rtt = ktime_us_delta(ktime_get_real(), packet->stamp);
> 			/*
> 			 * Garbage-collect older (irrelevant) entries:
> 			 */
> 			tfrc_tx_hist_purge(&packet->next);
> 		}
> 	
> 		return rtt;
> 	}
> 
> Just a suggestion.

I thought about that, but ccid3_hc_tx_packet_recv needs a timestamp some
lines below, when we reuse the ktime_get_real call.

- Arnaldo

Re: [RFC]: tfrc_tx_hist_rtt

[Gerrit Renker]

| > I wonder if one could go one step further and also take the timestamp
| > directly when looking up the previous history sample, e.g.
| > 
<snip>
| 
| I thought about that, but ccid3_hc_tx_packet_recv needs a timestamp some
| lines below, when we reuse the ktime_get_real call.
| 
Oh, of course - that was real stupid of me. I think it is even in two occasions where a 
timestamp is needed, below in the same function.

I am really hoping that some time there is a robust RFC1323-like algorithm,
this could solve all the RTT sampling for both CCID2 and CCID3 (also CCID4),
and then there would be a RTT available in the main module (e.g. for better
estimating the Close/CloseReq retransmission timeout).