Commit 8b67ad12 authored Sep 04, 2008 by Gerrit Renker

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>

parent d0c05fe4

net/dccp/ccids/lib/tfrc_equation.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -632,7 +632,15 @@ 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. "
		/*
		* 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 */