settings: zms: add a cache to accelerate write/delete

adding a lookup cache improves write and delete operation as it doesn't
look for the name in the storage if no hash collision exists or if the
entry is deleted.

Signed-off-by: Riadh Ghaddab <[email protected]>

Author: rghaddab

subsys/settings/Kconfig

@@ -47,6 +47,25 @@ config SETTINGS_ZMS
 	help
 	  Use ZMS as settings storage backend.
 
+if SETTINGS_ZMS
+
+config SETTINGS_ZMS_NAME_CACHE
+	bool "ZMS name lookup cache"
+	select SYS_HASH_FUNC32
+	help
+	  Enable ZMS lookup cache, used to reduce the Settings name
+	  lookup time by checking if its hash had a collision.
+
+config SETTINGS_ZMS_NAME_CACHE_SIZE
+	int "ZMS name lookup cache size"
+	default 128
+	range 1 $(UINT32_MAX)
+	depends on SETTINGS_ZMS_NAME_CACHE
+	help
+	  Number of entries in Settings ZMS name cache.
+
+endif # SETTINGS_ZMS
+
 config SETTINGS_FCB
 	bool "FCB"
 	depends on FCB

subsys/settings/include/settings/settings_zms.h

@@ -61,6 +61,12 @@ extern "C" {
 #define ZMS_HASH_TOTAL_MASK GENMASK(29, 1)
 #define ZMS_MAX_COLLISIONS  (BIT(CONFIG_SETTINGS_ZMS_MAX_COLLISIONS_BITS) - 1)
 
+#if CONFIG_SETTINGS_ZMS_NAME_CACHE
+#define ZMS_CACHE_EXIST(x)         (x & BIT(0))
+#define ZMS_CACHE_HAS_COLLISION(x) (x & BIT(1))
+#define ZMS_CACHE_IS_DELETED(x)    (x & BIT(2))
+#endif /* CONFIG_SETTINGS_ZMS_NAME_CACHE */
+
 /* some useful macros */
 #define ZMS_NAME_HASH_ID(x) ((x & ZMS_HASH_TOTAL_MASK) | BIT(31))
 #define ZMS_UPDATE_COLLISION_NUM(x, y)                                                             \
@@ -71,6 +77,14 @@ struct settings_zms {
 	struct settings_store cf_store;
 	struct zms_fs cf_zms;
 	const struct device *flash_dev;
+#if CONFIG_SETTINGS_ZMS_NAME_CACHE
+	struct {
+		uint32_t name_hash;
+		uint8_t flags;
+	} cache[CONFIG_SETTINGS_ZMS_NAME_CACHE_SIZE];
+
+	uint32_t cache_next;
+#endif
 	uint32_t last_hash_id;
 	uint32_t second_to_last_hash_id;
 	uint8_t hash_collision_num;

subsys/settings/src/settings_zms.c

@@ -146,6 +146,79 @@ static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
 	return rc;
 }
 
+#if CONFIG_SETTINGS_ZMS_NAME_CACHE
+static void settings_zms_cache_add(struct settings_zms *cf, uint32_t name_hash, uint8_t flags)
+{
+	cf->cache[cf->cache_next].name_hash = name_hash;
+	cf->cache[cf->cache_next++].flags = flags;
+
+	cf->cache_next %= CONFIG_SETTINGS_ZMS_NAME_CACHE_SIZE;
+}
+
+static uint8_t settings_zms_cache_match(struct settings_zms *cf, uint32_t name_hash)
+{
+	int cache_index;
+
+	if (!cf->cache_next) {
+		cache_index = CONFIG_SETTINGS_ZMS_NAME_CACHE_SIZE - 1;
+	} else {
+		cache_index = cf->cache_next - 1;
+	}
+
+	for (int i = 0; i < CONFIG_SETTINGS_ZMS_NAME_CACHE_SIZE; i++) {
+		/* we check cache from recent values to old values */
+		if (cf->cache[cache_index].name_hash != name_hash) {
+			cache_index--;
+			if (cache_index < 0) {
+				cache_index = CONFIG_SETTINGS_ZMS_NAME_CACHE_SIZE - 1;
+			}
+			continue;
+		}
+
+		/* set the BIT(0) to indicate that the name_hash exist in cache */
+		return cf->cache[cache_index].flags | BIT(0);
+	}
+
+	return 0;
+}
+#endif /* CONFIG_SETTINGS_ZMS_NAME_CACHE */
+
+static int settings_zms_delete(struct settings_zms *cf, uint32_t name_hash)
+{
+	int rc = 0;
+
+	rc = zms_delete(&cf->cf_zms, name_hash);
+	if (rc >= 0) {
+		rc = zms_delete(&cf->cf_zms, name_hash + ZMS_DATA_ID_OFFSET);
+	}
+	if (rc < 0) {
+		return rc;
+	}
+	rc = settings_zms_unlink_ll_node(cf, name_hash);
+	if (rc < 0) {
+		return rc;
+	}
+
+	/* Now delete the current linked list element */
+	rc = zms_delete(&cf->cf_zms, name_hash | 1);
+	if (rc < 0) {
+		return rc;
+	}
+
+#ifdef CONFIG_SETTINGS_ZMS_NAME_CACHE
+	/* Update the flag of the Settings entry in cache. */
+	uint8_t cache_flags = 0;
+
+	if (ZMS_COLLISION_NUM(name_hash) > 0) {
+		cache_flags |= BIT(1);
+	}
+	/* set the delete BIT(1) indicating that the entry is deleted. */
+	cache_flags |= BIT(2);
+	settings_zms_cache_add(cf, name_hash & ZMS_HASH_MASK, cache_flags);
+#endif
+	return rc;
+}
+
 static int settings_zms_load(struct settings_store *cs, const struct settings_load_arg *arg)
 {
 	int ret = 0;
@@ -199,6 +272,15 @@ static int settings_zms_load(struct settings_store *cs, const struct settings_lo
 			break;
 		}
 
+#if CONFIG_SETTINGS_ZMS_NAME_CACHE
+		uint8_t cache_flags = 0;
+
+		if (ZMS_COLLISION_NUM(ll_hash_id) > 0) {
+			cache_flags |= BIT(1);
+		}
+		settings_zms_cache_add(cf, ll_hash_id & ZMS_HASH_MASK, cache_flags);
+#endif
+
 		/* update next ll_hash_id */
 		ret = zms_read(&cf->cf_zms, ll_hash_id, &settings_element,
 			       sizeof(struct settings_hash_linked_list));
@@ -221,7 +303,6 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 	uint32_t collision_num = 0;
 	bool delete;
 	bool write_name;
-	bool hash_collision;
 	int rc = 0;
 	int first_available_hash_index = -1;
 
@@ -236,9 +317,22 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 	/* MSB is always 1 */
 	name_hash |= BIT(31);
 
+#ifdef CONFIG_SETTINGS_ZMS_NAME_CACHE
+	uint8_t cache_flags = 0;
+
+	cache_flags = settings_zms_cache_match(cf, name_hash & ZMS_HASH_MASK);
+	if (ZMS_CACHE_EXIST(cache_flags) && !ZMS_CACHE_HAS_COLLISION(cache_flags)) {
+		if (ZMS_CACHE_IS_DELETED(cache_flags)) {
+			write_name = true;
+		} else {
+			write_name = false;
+		}
+		goto no_hash_collision;
+	}
+#endif
+
 	/* Let's find out if there is no hash collisions in the storage */
 	write_name = true;
-	hash_collision = true;
 
 	for (int i = 0; i <= cf->hash_collision_num; i++) {
 		rc = zms_read(&cf->cf_zms, name_hash + i * LSB_GET(ZMS_COLLISIONS_MASK), &rdname,
@@ -295,7 +389,6 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 			/* hash doesn't exist, do not write anything here */
 			return 0;
 		}
-
 		rc = settings_zms_delete(cf, name_hash);
 		return rc;
 	}
@@ -341,6 +434,14 @@ static int settings_zms_save(struct settings_store *cs, const char *name, const
 		cf->second_to_last_hash_id = cf->last_hash_id;
 		cf->last_hash_id = name_hash | 1;
 	}
+#ifdef CONFIG_SETTINGS_ZMS_NAME_CACHE
+	/* Add the flags of the written settings entry in cache */
+	cache_flags = 0;
+	if (ZMS_COLLISION_NUM(name_hash) > 0) {
+		cache_flags |= BIT(1);
+	}
+	settings_zms_cache_add(cf, name_hash & ZMS_HASH_MASK, cache_flags);
+#endif /* CONFIG_SETTINGS_ZMS_NAME_CACHE */
 
 	return 0;
 }