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Refactor smartlist_choose_node_by_bandwidth to be less horrible.

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With this patch, I dump the old kludge of using magic negative
numbers to indicate unknown bandwidths.  I also compute each node's
weighted bandwidth exactly once, rather than computing it once in
a loop to compute the total weighted bandwidth and a second time in
a loop to find which one we picked.
This commit is contained in:
Nick Mathewson 2012-08-09 12:59:04 -04:00
parent 50aecc68ca
commit 9bfb274abb
1 changed files with 27 additions and 42 deletions
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69
src/or/routerlist.c
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@ -1922,15 +1922,17 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
{
unsigned int i;
unsigned int i_chosen;
int32_t *bandwidths;
uint64_t *bandwidths;
int is_exit;
int is_guard;
int is_fast;
uint64_t total_nonexit_bw = 0, total_exit_bw = 0, total_bw = 0;
uint64_t total_nonguard_bw = 0, total_guard_bw = 0;
uint64_t rand_bw, tmp;
double exit_weight;
double guard_weight;
int n_unknown = 0;
bitarray_t *fast_bits;
bitarray_t *exit_bits;
bitarray_t *guard_bits;
int me_idx = -1;
@ -1954,10 +1956,9 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
}
/* First count the total bandwidth weight, and make a list
* of each value. <0 means "unknown; no routerinfo." We use the
* bits of negative values to remember whether the router was fast (-x)&1
* and whether it was an exit (-x)&2 or guard (-x)&4. Yes, it's a hack. */
bandwidths = tor_malloc(sizeof(int32_t)*smartlist_len(sl));
* of each value. We use UINT64_MAX to indicate "unknown". */
bandwidths = tor_malloc_zero(sizeof(uint64_t)*smartlist_len(sl));
fast_bits = bitarray_init_zero(smartlist_len(sl));
exit_bits = bitarray_init_zero(smartlist_len(sl));
guard_bits = bitarray_init_zero(smartlist_len(sl));
@ -1965,7 +1966,6 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
SMARTLIST_FOREACH_BEGIN(sl, const node_t *, node) {
/* first, learn what bandwidth we think i has */
int is_known = 1;
int32_t flags = 0;
uint32_t this_bw = 0;
i = node_sl_idx;
@ -1978,12 +1978,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
if (node->rs->has_bandwidth) {
this_bw = kb_to_bytes(node->rs->bandwidth);
} else { /* guess */
/* XXX024 once consensuses always list bandwidths, we can take
* this guessing business out. -RD */
is_known = 0;
flags = node->rs->is_fast ? 1 : 0;
flags |= is_exit ? 2 : 0;
flags |= is_guard ? 4 : 0;
}
} else if (node->ri) {
/* Must be a bridge if we're willing to use it */
@ -1994,12 +1989,11 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
bitarray_set(exit_bits, i);
if (is_guard)
bitarray_set(guard_bits, i);
if (node->is_fast)
bitarray_set(fast_bits, i);
if (is_known) {
bandwidths[i] = (int32_t) this_bw;
/* Casting this_bw to int32_t is safe because both kb_to_bytes
and bridge_get_advertised_bandwidth_bounded limit it to below
INT32_MAX. */
tor_assert(bandwidths[i] >= 0);
bandwidths[i] = this_bw;
if (is_guard)
total_guard_bw += this_bw;
else
@ -2010,7 +2004,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
total_nonexit_bw += this_bw;
} else {
++n_unknown;
bandwidths[node_sl_idx] = -flags;
bandwidths[i] = UINT64_MAX;
}
} SMARTLIST_FOREACH_END(node);
@ -2028,12 +2022,12 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
avg_slow = 20000;
}
for (i=0; i<(unsigned)smartlist_len(sl); ++i) {
int32_t bw = bandwidths[i];
if (bw>=0)
if (bandwidths[i] != UINT64_MAX)
continue;
is_exit = ((-bw)&2);
is_guard = ((-bw)&4);
bandwidths[i] = ((-bw)&1) ? avg_fast : avg_slow;
is_fast = bitarray_is_set(fast_bits, i);
is_exit = bitarray_is_set(exit_bits, i);
is_guard = bitarray_is_set(guard_bits, i);
bandwidths[i] = is_fast ? avg_fast : avg_slow;
if (is_exit)
total_exit_bw += bandwidths[i];
else
@ -2048,6 +2042,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
/* If there's no bandwidth at all, pick at random. */
if (!(total_exit_bw+total_nonexit_bw)) {
tor_free(bandwidths);
tor_free(fast_bits);
tor_free(exit_bits);
tor_free(guard_bits);
return smartlist_choose(sl);
@ -2081,20 +2076,20 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
total_bw = 0;
sl_last_weighted_bw_of_me = 0;
for (i=0; i < (unsigned)smartlist_len(sl); i++) {
uint64_t bw;
tor_assert(bandwidths[i] < UINT64_MAX);
is_exit = bitarray_is_set(exit_bits, i);
is_guard = bitarray_is_set(guard_bits, i);
if (is_exit && is_guard)
bw = ((uint64_t)(bandwidths[i] * exit_weight * guard_weight));
bandwidths[i] = tor_llround(bandwidths[i] * exit_weight * guard_weight);
else if (is_guard)
bw = ((uint64_t)(bandwidths[i] * guard_weight));
bandwidths[i] = tor_llround(bandwidths[i] * guard_weight);
else if (is_exit)
bw = ((uint64_t)(bandwidths[i] * exit_weight));
else
bw = bandwidths[i];
total_bw += bw;
bandwidths[i] = tor_llround(bandwidths[i] * exit_weight);
total_bw += bandwidths[i];
if (i == (unsigned) me_idx)
sl_last_weighted_bw_of_me = bw;
sl_last_weighted_bw_of_me = bandwidths[i];
}
}
@ -2121,18 +2116,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
tmp = 0;
i_chosen = (unsigned)smartlist_len(sl);
for (i=0; i < (unsigned)smartlist_len(sl); i++) {
is_exit = bitarray_is_set(exit_bits, i);
is_guard = bitarray_is_set(guard_bits, i);
/* Weights can be 0 if not counting guards/exits */
if (is_exit && is_guard)
tmp += ((uint64_t)(bandwidths[i] * exit_weight * guard_weight));
else if (is_guard)
tmp += ((uint64_t)(bandwidths[i] * guard_weight));
else if (is_exit)
tmp += ((uint64_t)(bandwidths[i] * exit_weight));
else
tmp += bandwidths[i];
tmp += bandwidths[i];
if (tmp > rand_bw) {
i_chosen = i;
@ -2151,6 +2135,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
U64_PRINTF_ARG(rand_bw), U64_PRINTF_ARG(total_bw));
}
tor_free(bandwidths);
tor_free(fast_bits);
tor_free(exit_bits);
tor_free(guard_bits);
return smartlist_get(sl, i);