This fixes a bug in the reverse lookup of p, given a value f(p) (used in the
reverse-lookup of the first/synthetic loss interval in RFC 3448, 6.3.1):
instead of p, the function returned the smallest table 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 impact 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, and thus unnecessarily reducing the throughput.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/lib/tfrc_equation.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
--- a/net/dccp/ccids/lib/tfrc_equation.c
+++ b/net/dccp/ccids/lib/tfrc_equation.c
@@ -677,11 +677,11 @@ 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];
+ return TFRC_SMALLEST_P;
}
if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) {
DCCP_WARN("fvalue %d exceeds bounds!\n", fvalue);
- return 1000000;
+ return 1000000; /* The maximum: 100% scaled by 10^6 */
}
if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1]) {
-
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