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| author | Gerrit Renker <gerrit@erg.abdn.ac.uk> | 2006-12-03 17:52:41 +0100 |
|---|---|---|
| committer | Arnaldo Carvalho de Melo <acme@mandriva.com> | 2006-12-03 17:52:41 +0100 |
| commit | 006042d7e1a0aae35c9dd9eb8ec71fa379679adb (patch) | |
| tree | e0f7a4f351fbf147bd452ff45061245fd985f27d /net/dccp | |
| parent | [DCCP] tfrc: Add protection against invalid parameters to TFRC routines (diff) | |
| download | linux-006042d7e1a0aae35c9dd9eb8ec71fa379679adb.tar.xz linux-006042d7e1a0aae35c9dd9eb8ec71fa379679adb.zip | |
[DCCP] tfrc: Identify TFRC table limits and simplify code
This
* adds documentation about the lowest resolution that is possible within
the bounds of the current lookup table
* defines a constant TFRC_SMALLEST_P which defines this resolution
* issues a warning if a given value of p is below resolution
* combines two previously adjacent if-blocks of nearly identical
structure into one
This patch does not change the algorithm as such.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Diffstat (limited to 'net/dccp')
| -rw-r--r-- | net/dccp/ccids/lib/tfrc_equation.c | 27 |
1 files changed, 18 insertions, 9 deletions
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c index ef3233d45a61..0a4a3d2feba5 100644 --- a/net/dccp/ccids/lib/tfrc_equation.c +++ b/net/dccp/ccids/lib/tfrc_equation.c @@ -19,6 +19,7 @@ #define TFRC_CALC_X_ARRSIZE 500 #define TFRC_CALC_X_SPLIT 50000 /* 0.05 * 1000000, details below */ +#define TFRC_SMALLEST_P (TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE) /* TFRC TCP Reno Throughput Equation Lookup Table for f(p) @@ -68,7 +69,9 @@ granularity for the practically more relevant case of small values of p (up to 5%), the second column is used; the first one ranges up to 100%. This split corresponds to the value of q = TFRC_CALC_X_SPLIT. At the same time this also - determines the smallest resolution. + determines the smallest resolution possible with this lookup table: + + TFRC_SMALLEST_P = TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE The entire table is generated by: for(i=0; i < TFRC_CALC_X_ARRSIZE; i++) { @@ -79,7 +82,7 @@ With the given configuration, we have, with M = TFRC_CALC_X_ARRSIZE-1, lookup[0][0] = g(1000000/(M+1)) = 1000000 * f(0.2%) lookup[M][0] = g(1000000) = 1000000 * f(100%) - lookup[0][1] = g(TFRC_CALC_X_SPLIT/(M+1)) = 1000000 * f(0.01%) + lookup[0][1] = g(TFRC_SMALLEST_P) = 1000000 * f(0.01%) lookup[M][1] = g(TFRC_CALC_X_SPLIT) = 1000000 * f(5%) In summary, the two columns represent f(p) for the following ranges: @@ -616,15 +619,21 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p) return ~0U; } - if (p < TFRC_CALC_X_SPLIT) /* 0 <= p < 0.05 */ - index = (p / (TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE)) - 1; - else /* 0.05 <= p <= 1.00 */ - index = (p / (1000000 / TFRC_CALC_X_ARRSIZE)) - 1; + 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); + index = 0; + } else /* 0.0001 <= p <= 0.05 */ + index = p/TFRC_SMALLEST_P - 1; + + f = tfrc_calc_x_lookup[index][1]; + + } else { /* 0.05 < p <= 1.00 */ + index = p/(1000000/TFRC_CALC_X_ARRSIZE) - 1; - if (p >= TFRC_CALC_X_SPLIT) f = tfrc_calc_x_lookup[index][0]; - else - f = tfrc_calc_x_lookup[index][1]; + } /* The following computes X = s/(R*f(p)) in bytes per second. Since f(p) * and R are both scaled by 1000000, we need to multiply by 1000000^2. |