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r13959@catbus: nickm | 2007-07-28 18:09:56 -0400

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Use the correct formula to calculate exit weights.


svn:r10956
This commit is contained in:
Nick Mathewson 2007-07-28 22:14:39 +00:00
parent afe9f33d35
commit 76a408941c
3 changed files with 33 additions and 25 deletions
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3
ChangeLog
View File

@ -43,6 +43,9 @@ Changes in version 0.2.0.3-alpha - 2007-??-??
o Performance improvements:
- Be more aggressive with freeing buffer RAM or putting it on the
free lists.
- If exit bandwidth ever exceeds one third of total bandwidth, then
use the correct formula to weight exit nodes when choosing paths.
(Based on patch from Mike Perry.)
o Performance improvements (win32):
- Use Critical Sections rather than Mutexes for synchronizing threads

6
doc/spec/path-spec.txt
View File

@ -189,7 +189,11 @@ of their choices.
on the fraction of bandwidth available from non-Exit nodes. Call the
total clipped advertised bandwidth for Exit nodes under consideration E,
and the total clipped advertised bandwidth for non-Exit nodes under
consideration N. If E<N/2, we do not consider Exit-flagged nodes.
and the total clipped advertised bandwidth for all nodes under
consideration T. If E<T/3, we do not consider Exit-flagged nodes.
Otherwise, we weight their bandwidth with the factor 1-T/(3E). This
ensures that bandwidth is evenly distributed over nodes in 3-hop paths.
Otherwise, we weight their bandwidth with the factor (E-N/2)/(N+E-N/2) ==
(2E - N)/(2E + N). This ensures that bandwidth is evenly distributed over
nodes in 3-hop paths.

49
src/or/routerlist.c
View File

@ -1240,6 +1240,7 @@ smartlist_choose_by_bandwidth(smartlist_t *sl, int for_exit, int statuses)
double exit_weight;
int n_unknown = 0;
bitarray_t *exit_bits;
int include_exits = 1;
/* First count the total bandwidth weight, and make a list
* of each value. <0 means "unknown; no routerinfo." We use the
@ -1325,28 +1326,27 @@ smartlist_choose_by_bandwidth(smartlist_t *sl, int for_exit, int statuses)
/* If we're choosing an exit node, exit bandwidth counts fully. */
exit_weight = 1.0;
total_bw = total_exit_bw + total_nonexit_bw;
} else if (total_exit_bw < total_nonexit_bw / 2) {
/* If we're choosing a relay and exits are greatly outnumbered, ignore
* them. */
exit_weight = 0.0;
total_bw = total_nonexit_bw;
} else {
/* If we're choosing a relay and exits aren't outnumbered use the formula
* from path-spec. */
uint64_t leftover = (total_exit_bw - total_nonexit_bw / 2);
exit_weight = U64_TO_DBL(leftover) /
U64_TO_DBL(leftover + total_nonexit_bw);
#if 0
total_bw = total_nonexit_bw +
DBL_TO_U64(exit_weight * U64_TO_DBL(total_exit_bw));
#endif
total_bw = 0;
for (i=0; i < (unsigned)smartlist_len(sl); i++) {
is_exit = bitarray_is_set(exit_bits, i);
if (is_exit)
total_bw += ((uint64_t)(bandwidths[i] * exit_weight));
else
total_bw += bandwidths[i];
double all_bw = U64_TO_DBL(total_exit_bw+total_nonexit_bw);
double exit_bw = U64_TO_DBL(total_exit_bw);
/*
* For detailed derivation of this formula, see
* http://archives.seul.org/or/dev/Jul-2007/msg00056.html
*/
exit_weight = 1.0 - all_bw/(3.0*exit_bw);
if (exit_weight <= 0.0) {
include_exits = 0;
exit_weight = 0.0;
total_bw = total_nonexit_bw;
} else {
total_bw = 0;
for (i=0; i < (unsigned)smartlist_len(sl); i++) {
is_exit = bitarray_is_set(exit_bits, i);
if (is_exit)
total_bw += ((uint64_t)(bandwidths[i] * exit_weight));
else
total_bw += bandwidths[i];
}
}
}
/*
@ -1364,9 +1364,10 @@ smartlist_choose_by_bandwidth(smartlist_t *sl, int for_exit, int statuses)
tmp = 0;
for (i=0; i < (unsigned)smartlist_len(sl); i++) {
is_exit = bitarray_is_set(exit_bits, i);
if (is_exit)
tmp += ((uint64_t)(bandwidths[i] * exit_weight));
else
if (is_exit) {
if (include_exits)
tmp += ((uint64_t)(bandwidths[i] * exit_weight));
} else
tmp += bandwidths[i];
if (tmp >= rand_bw)
break;