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| author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2008-09-04 07:30:19 +0200 |
|---|---|---|
| committer | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2008-09-04 07:45:40 +0200 |
| commit | 8b67ad12b04ef7bdf5d2b4de24fe5a609b26cf12 (patch) | |
| tree | e434f1de89f42008020f6aa4767c0dc0b81c9e17 | |
| parent | d0c05fe4448db5cbdd886186860581f736f59ae9 (diff) | |
| download | op-kernel-dev-8b67ad12b04ef7bdf5d2b4de24fe5a609b26cf12.zip op-kernel-dev-8b67ad12b04ef7bdf5d2b4de24fe5a609b26cf12.tar.gz | |
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.c | 12 |
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; |
