From 1e8a287c79f64226541f5c44aa52d4698bb84cf5 Mon Sep 17 00:00:00 2001
From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Wed, 11 Jun 2008 11:19:10 +0100
Subject: dccp ccid-3: TFRC reverse-lookup Bug-Fix
This fixes a bug in the reverse lookup of p: given a value f(p), instead of p,
the function returned the smallest tabulated value f(p).
The smallest tabulated value of
10^6 * f(p) = sqrt(2*p/3) + 12 * sqrt(3*p/8) * (32 * p^3 + p)
for p=0.0001 is 8172.
Since this value is scaled by 10^6, the outcome of this bug is that a loss
of 8172/10^6 = 0.8172% was reported whenever the input was below the table
resolution of 0.01%.
This means that the value was over 80 times too high, resulting in large spikes
of the initial loss interval, thus unnecessarily reducing the throughput.
Also corrected the printk format (%u for u32).
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
net/dccp/ccids/lib/tfrc_equation.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
(limited to 'net/dccp/ccids/lib/tfrc_equation.c')
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c
index e4e64b76c10..2f20a29cffe 100644
--- a/net/dccp/ccids/lib/tfrc_equation.c
+++ b/net/dccp/ccids/lib/tfrc_equation.c
@@ -661,7 +661,7 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p)
EXPORT_SYMBOL_GPL(tfrc_calc_x);
-/*
+/**
* tfrc_calc_x_reverse_lookup - try to find p given f(p)
*
* @fvalue: function value to match, scaled by 1000000
@@ -676,11 +676,11 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue)
/* Error cases. */
if (fvalue < tfrc_calc_x_lookup[0][1]) {
- DCCP_WARN("fvalue %d smaller than resolution\n", fvalue);
- return tfrc_calc_x_lookup[0][1];
+ DCCP_WARN("fvalue %u smaller than resolution\n", fvalue);
+ return TFRC_SMALLEST_P;
}
if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) {
- DCCP_WARN("fvalue %d exceeds bounds!\n", fvalue);
+ DCCP_WARN("fvalue %u exceeds bounds!\n", fvalue);
return 1000000;
}
--
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