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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2008-09-04 07:30:19 +0200
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2008-09-04 07:45:40 +0200
commit8b67ad12b04ef7bdf5d2b4de24fe5a609b26cf12 (patch)
treee434f1de89f42008020f6aa4767c0dc0b81c9e17
parentd0c05fe4448db5cbdd886186860581f736f59ae9 (diff)
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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>
-rw-r--r--net/dccp/ccids/lib/tfrc_equation.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c
index bc3dc2b..38239c4 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;
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