From: Rusty Russell <rusty@rustcorp.com.au>
Date: Fri, 17 Jun 2022 04:33:53 +0000 (+0930)
Subject: htable: increase density from 75% to 87.5%
X-Git-Url: https://git.ozlabs.org/?a=commitdiff_plain;h=3fcc6bfb0447e07a69c4912951021a4104a6f726;p=ccan

htable: increase density from 75% to 87.5%

Across all benchmarks (on various sizes) this actually drops
performance by 3%.  However, density increasing by 15% is probably a
worthwhile tradeoff.

```
-Initial insert: 227-237(230+/-3.7) ns
+Initial insert: 266-281(273.4+/-6.5) ns
-Initial lookup (match): 65-66(65.4+/-0.49) ns
+Initial lookup (match): 67-78(70.6+/-3.8) ns
-Initial lookup (miss): 79-80(79.4+/-0.49) ns
+Initial lookup (miss): 82-93(84.8+/-4.2) ns
-Initial lookup (random): 111-115(112.6+/-1.6) ns
+Initial lookup (random): 118-138(123.4+/-7.4) ns
-Initial delete all: 66-68(66.6+/-0.8) ns
+Initial delete all: 79-90(82+/-4.1) ns
-Initial re-inserting: 87-90(88+/-1.3) ns
+Initial re-inserting: 104-116(107.2+/-4.4) ns
-Deleting first half: 32-33(32.4+/-0.49) ns
+Deleting first half: 37-43(39+/-2.1) ns
-Lookup after half-change (match): 67-69(68+/-0.89) ns
+Lookup after half-change (match): 72-81(74.2+/-3.4) ns
-Churning second time: 272-276(274.2+/-1.5) ns
+Churning second time: 304-332(310.2+/-11) ns
-Churning third time: 290-296(293+/-2) ns
+Churning third time: 233-259(239+/-10) ns
-Churning fourth time: 289-295(292+/-2.2) ns
+Churning fourth time: 309-337(315.6+/-11) ns
-Churning fifth time: 289-294(291.8+/-1.9) ns
+Churning fifth time: 307-337(315+/-11) ns
-Details: worst run 146 (24 deleted)
+Details: worst run 115 (2 deleted)
-Lookup after churn & spread (miss): 110-111(110.6+/-0.49) ns
+Lookup after churn & spread (miss): 93-104(95.4+/-4.3) ns
-Deleting half after churn & spread: 36-37(36.4+/-0.49) ns
+Deleting half after churn & spread: 39-45(40.4+/-2.3) ns
-Adding (a different) half after churn & spread: 81-82(81.6+/-0.49) ns
+Adding (a different) half after churn & spread: 38-43(39.6+/-1.7) ns
```

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---

diff --git a/ccan/htable/htable.c b/ccan/htable/htable.c
index 3247bea0..c5f166f8 100644
--- a/ccan/htable/htable.c
+++ b/ccan/htable/htable.c
@@ -86,14 +86,16 @@ void htable_init(struct htable *ht,
 	ht->table = &ht->common_bits;
 }
 
+/* Fill to 87.5% */
 static inline size_t ht_max(const struct htable *ht)
 {
-	return ((size_t)3 << ht->bits) / 4;
+	return ((size_t)7 << ht->bits) / 8;
 }
 
-static inline size_t ht_max_with_deleted(const struct htable *ht)
+/* Clean deleted if we're full, and more than 12.5% deleted */
+static inline size_t ht_max_deleted(const struct htable *ht)
 {
-	return ((size_t)9 << ht->bits) / 10;
+	return ((size_t)1 << ht->bits) / 8;
 }
 
 bool htable_init_sized(struct htable *ht,
@@ -103,7 +105,7 @@ bool htable_init_sized(struct htable *ht,
 	htable_init(ht, rehash, priv);
 
 	/* Don't go insane with sizing. */
-	for (ht->bits = 1; ((size_t)3 << ht->bits) / 4 < expect; ht->bits++) {
+	for (ht->bits = 1; ht_max(ht) < expect; ht->bits++) {
 		if (ht->bits == 30)
 			break;
 	}
@@ -379,10 +381,15 @@ bool htable_add_(struct htable *ht, size_t hash, const void *p)
 	assert(p);
 	assert(entry_is_valid((uintptr_t)p));
 
-	if (ht->elems+1 > ht_max(ht) && !double_table(ht))
-		return false;
-	if (ht->elems+1 + ht->deleted > ht_max_with_deleted(ht))
-		rehash_table(ht);
+	/* Getting too full? */
+	if (ht->elems+1 + ht->deleted > ht_max(ht)) {
+		/* If we're more than 1/8 deleted, clean those,
+		 * otherwise double table size. */
+		if (ht->deleted > ht_max_deleted(ht))
+			rehash_table(ht);
+		else if (!double_table(ht))
+			return false;
+	}
 	if (((uintptr_t)p & ht->common_mask) != ht->common_bits)
 		update_common(ht, p);