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dccp tfrc: Suppress unavoidable "below resolution" warning

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In the congestion-avoidance phase a decay of p towards 0 is natural once fewer
losses are encountered. Hence the warning message "p is below resolution" is
not necessary, and thus turned into a debug message by this patch.

The TFRC_SMALLEST_P is needed since in theory p never actually reaches 0. When
no further losses are encountered, the loss interval I_0 grows in length, 
causing p to decrease towards 0, causing X_calc = s/(RTT * f(p)) to increase.

With the given minimum-resolution this congestion avoidance phase stops at some
fixed value, an approximation formula has been added to the documentation.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This commit is contained in:
Gerrit Renker 2008-09-04 07:30:19 +02:00
parent d0c05fe444
commit 8b67ad12b0
1 changed files with 10 additions and 2 deletions
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12
net/dccp/ccids/lib/tfrc_equation.c
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@ -632,8 +632,16 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p)
if (p <= TFRC_CALC_X_SPLIT) { /* 0.0000 < p <= 0.05 */
if (p < TFRC_SMALLEST_P) { /* 0.0000 < p < 0.0001 */
DCCP_WARN("Value of p (%d) below resolution. "
"Substituting %d\n", p, TFRC_SMALLEST_P);
/*
* In the congestion-avoidance phase p decays towards 0
* when there are no further losses, so this case is
* natural. Truncating to p_min = 0.01% means that the
* maximum achievable throughput is limited to about
* X_calc_max = 122.4 * s/RTT (see RFC 3448, 3.1); e.g.
* with s=1500 bytes, RTT=0.01 s: X_calc_max = 147 Mbps.
*/
tfrc_pr_debug("Value of p (%d) below resolution. "
"Substituting %d\n", p, TFRC_SMALLEST_P);
index = 0;
} else /* 0.0001 <= p <= 0.05 */
index = p/TFRC_SMALLEST_P - 1;