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dccp tfrc: Suppress unavoidable "below resolution" warning
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>
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1 changed files with 10 additions and 2 deletions
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@ -632,8 +632,16 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p)
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if (p <= TFRC_CALC_X_SPLIT) { /* 0.0000 < p <= 0.05 */
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if (p < TFRC_SMALLEST_P) { /* 0.0000 < p < 0.0001 */
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DCCP_WARN("Value of p (%d) below resolution. "
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"Substituting %d\n", p, TFRC_SMALLEST_P);
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/*
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* In the congestion-avoidance phase p decays towards 0
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* when there are no further losses, so this case is
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* natural. Truncating to p_min = 0.01% means that the
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* maximum achievable throughput is limited to about
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* X_calc_max = 122.4 * s/RTT (see RFC 3448, 3.1); e.g.
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* with s=1500 bytes, RTT=0.01 s: X_calc_max = 147 Mbps.
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*/
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tfrc_pr_debug("Value of p (%d) below resolution. "
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"Substituting %d\n", p, TFRC_SMALLEST_P);
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index = 0;
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} else /* 0.0001 <= p <= 0.05 */
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index = p/TFRC_SMALLEST_P - 1;
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