From 8b67ad12b04ef7bdf5d2b4de24fe5a609b26cf12 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Thu, 4 Sep 2008 07:30:19 +0200 Subject: 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 --- net/dccp/ccids/lib/tfrc_equation.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) (limited to 'net/dccp/ccids') diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c index bc3dc2b2a849..38239c4d5e14 100644 --- a/net/dccp/ccids/lib/tfrc_equation.c +++ b/net/dccp/ccids/lib/tfrc_equation.c @@ -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; -- cgit v1.2.3