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dijkstra: fix heap ordering.

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We were always ordering heap by distance, not score (which are different
if we are routing by cheapest, not shortest!).

This simplifies our callbacks, too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2020-10-20 14:28:06 +10:30
parent 4a1843a151
commit 1bf3eebbf6
6 changed files with 49 additions and 85 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
common/dijkstra.c
View File

@ -22,6 +22,9 @@ struct dijkstra {
/* NULL means it's been visited already. */
const struct gossmap_node **heapptr;
/* How we decide "best" */
u64 score;
/* We could re-evaluate to determine this, but keeps it simple */
struct gossmap_chan *best_chan;
};
@ -67,9 +70,9 @@ static int less_comparer(const void *const ctx,
const void *const b)
{
return get_dijkstra(global_dijkstra, global_map,
*(struct gossmap_node **)a)->distance
*(struct gossmap_node **)a)->score
> get_dijkstra(global_dijkstra, global_map,
*(struct gossmap_node **)b)->distance;
*(struct gossmap_node **)b)->score;
}
static void item_mover(void *const dst, const void *const src)
@ -101,6 +104,7 @@ static const struct gossmap_node **mkheap(const tal_t *ctx,
d->distance = 0;
d->total_delay = 0;
d->cost = sent;
d->score = 0;
i--;
} else {
heap[i] = n;
@ -108,6 +112,7 @@ static const struct gossmap_node **mkheap(const tal_t *ctx,
d->distance = UINT_MAX;
d->cost = AMOUNT_MSAT(-1ULL);
d->total_delay = 0;
d->score = -1ULL;
}
}
assert(i == tal_count(heap));
@ -142,13 +147,9 @@ dijkstra_(const tal_t *ctx,
int dir,
struct amount_msat amount,
void *arg),
bool (*path_better)(u32 old_distance,
u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *arg),
u64 (*path_score)(u32 distance,
struct amount_msat cost,
struct amount_msat risk),
void *arg)
{
struct dijkstra *dij;
@ -229,7 +230,8 @@ dijkstra_(const tal_t *ctx,
int which_half;
struct gossmap_chan *c;
struct dijkstra *d;
struct amount_msat cost, new_risk, old_risk;
struct amount_msat cost, risk;
u64 score;
c = gossmap_nth_chan(map, cur, i, &which_half);
neighbor = gossmap_nth_node(map, c, !which_half);
@ -251,20 +253,11 @@ dijkstra_(const tal_t *ctx,
continue;
/* cltv_delay can't overflow: only 20 bits per hop. */
new_risk = risk_price(cost, riskfactor,
risk = risk_price(cost, riskfactor,
cur_d->total_delay
+ c->half[!which_half].delay);
old_risk = risk_price(d->cost, riskfactor,
d->total_delay);
if (!path_better(d->distance,
cur_d->distance + 1,
d->cost,
cost,
old_risk,
new_risk,
arg))
score = path_score(cur_d->distance + 1, cost, risk);
if (score >= d->score)
continue;
d->distance = cur_d->distance + 1;
@ -272,6 +265,7 @@ dijkstra_(const tal_t *ctx,
+ c->half[!which_half].delay;
d->cost = cost;
d->best_chan = c;
d->score = score;
gheap_restore_heap_after_item_increase(&gheap_ctx,
heap, heapsize,
d->heapptr - heap);

19
common/dijkstra.h
View File

@ -21,28 +21,19 @@ dijkstra_(const tal_t *ctx,
int dir,
struct amount_msat amount,
void *arg),
bool (*path_better)(u32 old_distance,
u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *arg),
u64 (*path_score)(u32 distance,
struct amount_msat cost,
struct amount_msat risk),
void *arg);
#define dijkstra(ctx, map, start, amount, riskfactor, channel_ok, \
path_better, arg) \
path_score, arg) \
dijkstra_((ctx), (map), (start), (amount), (riskfactor), \
typesafe_cb_preargs(bool, void *, (channel_ok), (arg), \
const struct gossmap *, \
const struct gossmap_chan *, \
int, struct amount_msat), \
typesafe_cb_preargs(bool, void *, (path_better), (arg), \
u32, u32, \
struct amount_msat, \
struct amount_msat, \
struct amount_msat, \
struct amount_msat), \
(path_score), \
(arg))
/* Returns UINT_MAX if unreachable. */

47
common/route.c
View File

@ -37,43 +37,28 @@ bool route_can_carry(const struct gossmap *map,
return route_can_carry_even_disabled(map, c, dir, amount, arg);
}
bool route_path_shorter(u32 old_distance, u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *unused)
/* Prioritize distance over costs */
u64 route_score_shorter(u32 distance,
struct amount_msat cost,
struct amount_msat risk)
{
if (new_distance > old_distance)
return false;
if (new_distance < old_distance)
return true;
u64 costs = cost.millisatoshis + risk.millisatoshis; /* Raw: score */
if (costs > 0xFFFFFFFF)
costs = 0xFFFFFFFF;
/* Tiebreak by cost */
if (!amount_msat_add(&old_cost, old_cost, old_risk)
|| !amount_msat_add(&new_cost, new_cost, new_risk))
return false;
return amount_msat_less(new_cost, old_cost);
return costs + ((u64)distance << 32);
}
bool route_path_cheaper(u32 old_distance, u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *unused)
/* Prioritize costs over distance */
u64 route_score_cheaper(u32 distance,
struct amount_msat cost,
struct amount_msat risk)
{
if (!amount_msat_add(&old_cost, old_cost, old_risk)
|| !amount_msat_add(&new_cost, new_cost, new_risk))
return false;
u64 costs = cost.millisatoshis + risk.millisatoshis; /* Raw: score */
if (costs > 0xFFFFFFFF)
costs = 0xFFFFFFFF;
if (amount_msat_greater(new_cost, old_cost))
return false;
if (amount_msat_less(new_cost, old_cost))
return true;
/* Tiebreak by distance */
return new_distance < old_distance;
return (costs << 32) + distance;
}
struct route **route_from_dijkstra(const struct gossmap *map,

18
common/route.h
View File

@ -27,20 +27,14 @@ bool route_can_carry_even_disabled(const struct gossmap *map,
void *unused);
/* Shortest path, with lower amount tiebreak */
bool route_path_shorter(u32 old_distance, u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *unused);
u64 route_score_shorter(u32 distance,
struct amount_msat cost,
struct amount_msat risk);
/* Cheapest path, with shorter path tiebreak */
bool route_path_cheaper(u32 old_distance, u32 new_distance,
struct amount_msat old_cost,
struct amount_msat new_cost,
struct amount_msat old_risk,
struct amount_msat new_risk,
void *unused);
u64 route_score_cheaper(u32 distance,
struct amount_msat cost,
struct amount_msat risk);
/* Extract route tal_arr from completed dijkstra */
struct route **route_from_dijkstra(const struct gossmap *map,

2
devtools/route.c
View File

@ -52,7 +52,7 @@ static struct route **least_cost(struct gossmap *map,
tstart = time_mono();
dij = dijkstra(tmpctx, map, dst,
sent, riskfactor, route_can_carry,
route_path_cheaper, NULL);
route_score_cheaper, NULL);
tstop = time_mono();
printf("# Time to find route: %"PRIu64" usec\n",

6
devtools/topology.c
View File

@ -55,7 +55,7 @@ static size_t count_possible_sources(const struct gossmap *map,
size_t distance_budget, num;
dij = dijkstra(tmpctx, map, n, AMOUNT_MSAT(0), 0,
channel_usable_to_excl, route_path_shorter, exclude);
channel_usable_to_excl, route_score_shorter, exclude);
if (is_last_node)
distance_budget = ROUTING_MAX_HOPS - 1;
@ -132,7 +132,7 @@ static size_t count_possible_destinations(const struct gossmap *map,
size_t distance_budget, num;
dij = dijkstra(tmpctx, map, start, AMOUNT_MSAT(0), 0,
channel_usable_from_excl, route_path_shorter, exclude);
channel_usable_from_excl, route_score_shorter, exclude);
if (is_first_node)
distance_budget = ROUTING_MAX_HOPS - 1;
@ -191,7 +191,7 @@ static bool measure_least_cost(struct gossmap *map,
tstart = time_mono();
dij = dijkstra(tmpctx, map, dst,
sent, riskfactor, channel_usable,
route_path_cheaper, NULL);
route_score_cheaper, NULL);
tstop = time_mono();
printf("# Time to find path: %"PRIu64" usec\n",