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askrene: use a simple array as our queue.

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We only ever visit each node once, so we can just use an array.  This
avoids calling tal() all the time, which is *especially* slow when we're
memory tracking.

I had an old canned gossmap which I benchmarked for these (and in
particular one node was unreachable, and that was slow):

Before: 17.27 seconds
After: 5.80 seconds

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2024-10-02 16:50:25 +09:30
parent 79fa3d3d7a
commit 9f0c0e1cca
1 changed files with 10 additions and 24 deletions
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34
plugins/askrene/mcf.c
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@ -2,7 +2,6 @@
#include <assert.h>
#include <ccan/bitmap/bitmap.h>
#include <ccan/list/list.h>
#include <ccan/lqueue/lqueue.h>
#include <ccan/tal/str/str.h>
#include <ccan/tal/tal.h>
#include <common/utils.h>
@ -687,13 +686,6 @@ init_linear_network(const tal_t *ctx, const struct pay_parameters *params)
return linear_network;
}
/* Simple queue to traverse the network. */
struct queue_data
{
u32 idx;
struct lqueue_link ql;
};
// TODO(eduardo): unit test this
/* Finds an admissible path from source to target, traversing arcs in the
* residual network with capacity greater than 0.
@ -705,25 +697,21 @@ find_admissible_path(const struct linear_network *linear_network,
const u32 source, const u32 target, struct arc *prev)
{
bool target_found = false;
/* Simple linear queue of node indexes */
u32 *queue = tal_arr(tmpctx, u32, linear_network->max_num_arcs);
size_t qstart, qend;
for(size_t i=0;i<tal_count(prev);++i)
prev[i].idx=INVALID_INDEX;
// The graph is dense, and the farthest node is just a few hops away,
// hence let's BFS search.
LQUEUE(struct queue_data,ql) myqueue = LQUEUE_INIT;
struct queue_data *qdata;
queue[0] = source;
qstart = 0;
qend = 1;
qdata = tal(tmpctx, struct queue_data);
qdata->idx = source;
lqueue_enqueue(&myqueue,qdata);
while(!lqueue_empty(&myqueue))
{
qdata = lqueue_dequeue(&myqueue);
u32 cur = qdata->idx;
tal_free(qdata);
while (qstart < qend) {
u32 cur = queue[qstart++];
if(cur==target)
{
@ -748,10 +736,8 @@ find_admissible_path(const struct linear_network *linear_network,
continue;
prev[next] = arc;
qdata = tal(tmpctx, struct queue_data);
qdata->idx = next;
lqueue_enqueue(&myqueue,qdata);
assert(qend < linear_network->max_num_arcs);
queue[qend++] = next;
}
}
return target_found;