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List:       dccp
Subject:    RE: [CCID-4] [Patch 1/1]: Bug fix - no header penalty during slow-start
From:       "Roksana Boreli" <Roksana.Boreli () nicta ! com ! au>
Date:       2008-05-15 3:18:15
Message-ID: 09D3F703EF3B0A4CBE28449EA9F3D32009EB4FC3 () nicta-atp-mail ! in ! nicta ! com ! au
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Thanks very much that's fine (and sorry for us not acting on it
earlier). 


Kind regards, Roksana


-----Original Message-----
From: Gerrit Renker [mailto:gerrit@erg.abdn.ac.uk] 
Sent: Wednesday, 14 May 2008 7:16 PM
To: Babil
Cc: Roksana Boreli; dccp@vger.kernel.org; Emmanuel Lochin (External)
Subject: [CCID-4] [Patch 1/1]: Bug fix - no header penalty during
slow-start

I haven't heard back so I put the following patch corresponding to your
description at the top of the ccid4 subtree. I can easily replace it if
people wanted this differently.

-------------------------> Patch 
-------------------------> <------------------------------------------
[CCID4]: No header penalty in slow-start

Bug fix reported by Roksana Boreli on 12/5/2008: header penalty was
incorrectly applied during slow-start.

For packet sizes s this meant that the slow-start degenerated into an
exponential decrease, due to

 X_0   = RFC3390 initial rate
 X_i+1 = 2 / (1 + 36/s) * X_i	; for i >= 1

When s < 36, the multiplicative factor is less than 1, causing a
reduction of X each time during slow start.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/ccids/ccid4.c |   19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

--- a/net/dccp/ccids/ccid4.c
+++ b/net/dccp/ccids/ccid4.c
@@ -93,17 +93,6 @@ static void ccid4_update_send_interval(s  }
 
 /**
- * ccid4_hc_tx_x_header_penalty  -  Update allowed sending rate X
- * @hctx: half-connection to adjust
- * This function adjusts sending rate according to [TFRC-SP, Section 5]
- */
-static inline void ccid4_hc_tx_x_header_penalty(struct tfrc_hc_tx_sock
*hctx) -{
-	hctx->x *= hctx->s;
-	do_div(hctx->x, (hctx->s + CCID4HCTX_H));
-}
-
-/**
  * ccid4_hc_tx_update_x  -  Update allowed sending rate X
  * @stamp: most recent time if available - can be left NULL.
  * This function tracks draft rfc3448bis, check there for latest
details.
@@ -136,14 +125,18 @@ static void ccid4_hc_tx_update_x(struct 
 
 		hctx->x = min(((u64)hctx->x_calc) << 6, min_rate);
 		low_thresh /= TFRC_T_MBI;
-		ccid4_hc_tx_x_header_penalty(hctx);
+		/*
+		 * CCID-4 Header Penalty:
+		 * Adjust sending rate according to [TFRC-SP, Section 5]
+		 */
+		hctx->x *= hctx->s;
+		do_div(hctx->x, hctx->s + CCID4HCTX_H);
 
 	} else if (ktime_us_delta(now, hctx->t_ld) - (s64)hctx->rtt >=
0) {
 
 		hctx->x    = min(2 * old_x, min_rate);
 		low_thresh = scaled_div(low_thresh, hctx->rtt);
 		hctx->t_ld = now;
-		ccid4_hc_tx_x_header_penalty(hctx);
 	}
 
 	if (hctx->x != old_x) {

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