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hodec2: cosmetic: clarify afs_bias, simplify pick_better_lchan_to_move() 

Instead of passing the TCH/H -> TCH/F bias (AFS bias) in local
variables, rather store it in the ho_candidate struct next to the other
rxlev related values.

Add the AFS bias to the compared rxlev in pick_better_lchan_to_move().

Modify pick_better_lchan_to_move() to simpler semantics of returning
either a or b.

No functional change.

Change-Id: I73860abdf2a77270ca4851ad58c09767d1bb08f1
This commit is contained in:
Neels Hofmeyr 2021-01-02 21:19:55 +01:00
parent 0c01ab6cbb
commit 305f21f9dc
1 changed files with 36 additions and 50 deletions
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86
src/osmo-bsc/handover_decision_2.c
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@ -106,6 +106,7 @@ struct ho_candidate {
uint8_t requirements; /* what is fulfilled */
int rxlev_current;
int rxlev_target;
int rxlev_afs_bias;
};
enum ho_reason {
@ -1398,63 +1399,55 @@ static bool is_upgrade_to_tchf(const struct ho_candidate *c, uint8_t for_require
/* Given two candidates, pick the one that should rather be moved during handover.
* Return the better candidate in out-parameters best_cand and best_avg_db.
*/
static bool pick_better_lchan_to_move(bool want_highest_db,
struct ho_candidate **best_cand_p, unsigned int *best_avg_db_p,
struct ho_candidate *other_cand, unsigned int other_avg_db)
static struct ho_candidate *pick_better_lchan_to_move(bool want_highest_db,
struct ho_candidate *a,
struct ho_candidate *b)
{
if (!*best_cand_p)
goto return_other;
int a_rxlev;
int b_rxlev;
if (want_highest_db && (*best_avg_db_p < other_avg_db))
goto return_other;
if (!want_highest_db && (*best_avg_db_p > other_avg_db))
goto return_other;
if (!a)
return b;
if (!b)
return a;
a_rxlev = a->rxlev_target + a->rxlev_afs_bias;
b_rxlev = b->rxlev_target + b->rxlev_afs_bias;
if (want_highest_db && a_rxlev < b_rxlev)
return b;
if (!want_highest_db && a_rxlev > b_rxlev)
return b;
/* The two lchans have identical ratings, prefer picking a dynamic timeslot: free PDCH and allow more timeslot
* type flexibility for further congestion resolution. */
if (lchan_is_on_dynamic_ts(other_cand->lchan)) {
if (lchan_is_on_dynamic_ts(b->lchan)) {
/* If both are dynamic, prefer one that completely (or to a higher degree) frees its timeslot. */
if (lchan_is_on_dynamic_ts((*best_cand_p)->lchan)
&& ts_usage_count((*best_cand_p)->lchan->ts) < ts_usage_count(other_cand->lchan->ts))
return false;
if (lchan_is_on_dynamic_ts(a->lchan)
&& ts_usage_count(a->lchan->ts) < ts_usage_count(b->lchan->ts))
return a;
/* If both equally satisfy these preferences, it does not matter which one is picked.
* Give slight preference to moving later dyn TS, so that a free dyn TS may group with following static
* PDCH, though this depends on how the user configured the TS -- not harmful to do so anyway. */
goto return_other;
return b;
}
/* keep the same candidate. */
return false;
return_other:
*best_cand_p = other_cand;
*best_avg_db_p = other_avg_db;
return true;
return a;
}
static struct ho_candidate *pick_best_candidate(int *applied_afs_bias,
struct ho_candidate *clist, int clist_len,
static struct ho_candidate *pick_best_candidate(struct ho_candidate *clist, int clist_len,
bool want_highest_db,
bool omit_intra_cell_upgrade_to_tchf,
bool only_intra_cell_upgrade_to_tchf,
uint8_t for_requirement)
{
struct ho_candidate *result = NULL;
unsigned int result_avg_rxlev;
int result_afs_bias = 0;
int i;
if (applied_afs_bias)
*applied_afs_bias = 0;
result_avg_rxlev = want_highest_db ? 0 : INT_MAX;
for (i = 0; i < clist_len; i++) {
struct ho_candidate *c = &clist[i];
bool intra_cell;
bool upgrade_to_tch_f;
int avg_rxlev;
int afs_bias;
/* For multiple passes of congestion resolution, already handovered candidates are marked by lchan =
* NULL. (though at the time of writing, multiple passes of congestion resolution are DISABLED.) */
@ -1478,21 +1471,15 @@ static struct ho_candidate *pick_best_candidate(int *applied_afs_bias,
&& (intra_cell && upgrade_to_tch_f))
continue;
avg_rxlev = c->rxlev_target;
/* improve AHS */
if (upgrade_to_tch_f)
afs_bias = ho_get_hodec2_afs_bias_rxlev(c->bts->ho);
c->rxlev_afs_bias = ho_get_hodec2_afs_bias_rxlev(c->bts->ho);
else
afs_bias = 0;
avg_rxlev += afs_bias;
c->rxlev_afs_bias = 0;
if (pick_better_lchan_to_move(want_highest_db, &result, &result_avg_rxlev, c, avg_rxlev))
result_afs_bias = afs_bias;
result = pick_better_lchan_to_move(want_highest_db, result, c);
}
if (applied_afs_bias)
*applied_afs_bias = result_afs_bias;
return result;
}
@ -1556,7 +1543,6 @@ static int bts_resolve_congestion(struct gsm_bts *bts, int tchf_congestion, int
struct ho_candidate *best_cand = NULL;
int rc = 0;
int any_ho = 0;
int is_improved = 0;
if (tchf_congestion < 0)
tchf_congestion = 0;
@ -1657,7 +1643,7 @@ next_b1:
/* TODO: attempt inter-BSC HO if no local cells qualify, and rely on the remote BSS to
* deny receiving the handover if it also considers itself congested. Maybe do that only
* when the cell is absolutely full, i.e. not only min-free-slots. (x) */
best_cand = pick_best_candidate(&is_improved, clist, candidates,
best_cand = pick_best_candidate(clist, candidates,
/* want_highest_db */ true,
/* omit_intra_cell_upgrade_to_tchf */ true,
/* only_intra_cell_upgrade_to_tchf */ false,
@ -1666,7 +1652,7 @@ next_b1:
any_ho = 1;
LOGPHOCAND(best_cand, LOGL_DEBUG, "Best candidate: RX level %d%s\n",
rxlev2dbm(best_cand->rxlev_target),
is_improved ? " (applied AHS->AFS bias)" : "");
best_cand->rxlev_afs_bias ? " (applied AHS->AFS bias)" : "");
trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_B_MASK);
#if 0
/* if there is still congestion, mark lchan as deleted
@ -1698,7 +1684,7 @@ next_b2:
* but simply pick the lowest one.
* Upgrading TCH/H channels obviously only applies when TCH/H is actually congested. */
if (tchh_congestion > 0)
best_cand = pick_best_candidate(&is_improved, clist, candidates,
best_cand = pick_best_candidate(clist, candidates,
/* want_highest_db */ false,
/* omit_intra_cell_upgrade_to_tchf */ false,
/* only_intra_cell_upgrade_to_tchf */ true,
@ -1707,7 +1693,7 @@ next_b2:
any_ho = 1;
LOGPHOCAND(best_cand, LOGL_INFO, "Worst candidate: RX level %d from TCH/H -> TCH/F%s\n",
rxlev2dbm(best_cand->rxlev_target),
is_improved ? " (applied AHS -> AFS rxlev bias)" : "");
best_cand->rxlev_afs_bias ? " (applied AHS -> AFS rxlev bias)" : "");
trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_B_MASK);
#if 0
/* if there is still congestion, mark lchan as deleted
@ -1733,7 +1719,7 @@ next_c1:
/* Select best candidate that balances congestion.
* Again no remote BSS.
* Again no TCH/H -> F upgrades within the same cell. */
best_cand = pick_best_candidate(&is_improved, clist, candidates,
best_cand = pick_best_candidate(clist, candidates,
/* want_highest_db */ true,
/* omit_intra_cell_upgrade_to_tchf */ true,
/* only_intra_cell_upgrade_to_tchf */ false,
@ -1742,7 +1728,7 @@ next_c1:
any_ho = 1;
LOGPHOCAND(best_cand, LOGL_INFO, "Best candidate: RX level %d%s\n",
rxlev2dbm(best_cand->rxlev_target),
is_improved ? " (applied AHS -> AFS rxlev bias)" : "");
best_cand->rxlev_afs_bias ? " (applied AHS -> AFS rxlev bias)" : "");
trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_C_MASK);
#if 0
/* if there is still congestion, mark lchan as deleted
@ -1774,7 +1760,7 @@ next_c2:
/* Look for upgrading TCH/H to TCH/F within the same cell, which balances congestion, again upgrade the TCH/H
* lchan that has the worst reception: */
if (tchh_congestion > 0)
best_cand = pick_best_candidate(&is_improved, clist, candidates,
best_cand = pick_best_candidate(clist, candidates,
/* want_highest_db */ false,
/* omit_intra_cell_upgrade_to_tchf */ false,
/* only_intra_cell_upgrade_to_tchf */ true,
@ -1785,7 +1771,7 @@ next_c2:
any_ho = 1;
LOGPHOCAND(best_cand, LOGL_INFO, "Worst candidate: RX level %d from TCH/H -> TCH/F%s\n",
rxlev2dbm(best_cand->rxlev_target),
is_improved ? " (applied AHS -> AFS rxlev bias)" : "");
best_cand->rxlev_afs_bias ? " (applied AHS -> AFS rxlev bias)" : "");
trigger_ho(best_cand, best_cand->requirements & REQUIREMENT_C_MASK);
#if 0
/* if there is still congestion, mark lchan as deleted