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Date:	Tue, 15 Apr 2008 15:43:52 -0400
From:	Allan Stephens <allan.stephens@...driver.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, allan.stephens@...driver.com
Subject: [PATCH 2/7 net-2.6.26] [TIPC]: Optimized initialization of TIPC reference table

This patch optimizes the initialization phase of TIPC's reference
table, so that it initializes table entries on an "as needed" basis.
(Previously, all entries of the table were initialized, regardless
of whether they actually ended up being used.)

Signed-off-by: Allan Stephens <allan.stephens@...driver.com>
---
 net/tipc/ref.c |  128 ++++++++++++++++++++++++++++++++++----------------------
 1 files changed, 78 insertions(+), 50 deletions(-)

diff --git a/net/tipc/ref.c b/net/tipc/ref.c
index 9c2eb9b..75cfb8d 100644
--- a/net/tipc/ref.c
+++ b/net/tipc/ref.c
@@ -50,7 +50,7 @@
  * struct reference - TIPC object reference entry
  * @object: pointer to object associated with reference entry
  * @lock: spinlock controlling access to object
- * @data: reference value associated with object (or link to next unused entry)
+ * @data: reference value for object (combines instance & array index info)
  */
 
 struct reference {
@@ -65,31 +65,40 @@ struct reference {
 /**
  * struct tipc_ref_table - table of TIPC object reference entries
  * @entries: pointer to array of reference entries
- * @index_mask: bitmask for array index portion of reference values
+ * @capacity: array index of first unusable entry
+ * @init_point: array index of first uninitialized entry
  * @first_free: array index of first unused object reference entry
  * @last_free: array index of last unused object reference entry
+ * @index_mask: bitmask for array index portion of reference values
+ * @start_mask: initial value for instance value portion of reference values
  */
 
 struct ref_table {
 	struct reference *entries;
-	u32 index_mask;
+	u32 capacity;
+	u32 init_point;
 	u32 first_free;
 	u32 last_free;
+	u32 index_mask;
+	u32 start_mask;
 };
 
 /*
  * Object reference table consists of 2**N entries.
  *
- * A used entry has object ptr != 0, reference == XXXX|own index
- *				     (XXXX changes each time entry is acquired)
- * A free entry has object ptr == 0, reference == YYYY|next free index
- *				     (YYYY is one more than last used XXXX)
+ * State	Object ptr	Reference
+ * -----        ----------      ---------
+ * In use        non-NULL       XXXX|own index
+ *				(XXXX changes each time entry is acquired)
+ * Free            NULL         YYYY|next free index
+ *				(YYYY is one more than last used XXXX)
+ * Uninitialized   NULL         0
  *
- * Free list is initially chained from entry (2**N)-1 to entry 1.
- * Entry 0 is not used to allow index 0 to indicate the end of the free list.
+ * Entry 0 is not used; this allows index 0 to denote the end of the free list.
  *
- * Note: Any accidental reference of the form XXXX|0--0 won't match entry 0
- * because entry 0's reference field has the form XXXX|1--1.
+ * Note that a reference value of 0 does not necessarily indicate that an
+ * entry is uninitialized, since the last entry in the free list could also
+ * have a reference value of 0 (although this is unlikely).
  */
 
 static struct ref_table tipc_ref_table = { NULL };
@@ -97,35 +106,33 @@ static struct ref_table tipc_ref_table = { NULL };
 static DEFINE_RWLOCK(ref_table_lock);
 
 /**
- * tipc_ref_table_init - create reference table for objects
+ * tipc_ref_table_init - initialize reference table for objects
  */
 
 int tipc_ref_table_init(u32 requested_size, u32 start)
 {
 	struct reference *table;
-	u32 sz = 1 << 4;
-	u32 index_mask;
-	int i;
+	u32 actual_size;
 
-	while (sz < requested_size) {
-		sz <<= 1;
-	}
-	table = vmalloc(sz * sizeof(*table));
+	/* account for unused entry, then round up size to a power of 2 */
+
+	requested_size++;
+	for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
+		/* do nothing */ ;
+
+	table = vmalloc(actual_size * sizeof(struct reference));
 	if (table == NULL)
 		return -ENOMEM;
 
-	write_lock_bh(&ref_table_lock);
-	index_mask = sz - 1;
-	for (i = sz - 1; i >= 0; i--) {
-		table[i].object = NULL;
-		spin_lock_init(&table[i].lock);
-		table[i].data.next_plus_upper = (start & ~index_mask) + i - 1;
-	}
+	memset(table, 0, actual_size * sizeof(struct reference));
 	tipc_ref_table.entries = table;
-	tipc_ref_table.index_mask = index_mask;
-	tipc_ref_table.first_free = sz - 1;
-	tipc_ref_table.last_free = 1;
-	write_unlock_bh(&ref_table_lock);
+	tipc_ref_table.capacity = requested_size;
+	tipc_ref_table.init_point = 1;
+	tipc_ref_table.first_free = 0;
+	tipc_ref_table.last_free = 0;
+	tipc_ref_table.index_mask = actual_size - 1;
+	tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;
+
 	return TIPC_OK;
 }
 
@@ -156,7 +163,7 @@ u32 tipc_ref_acquire(void *object, spinlock_t **lock)
 	u32 index;
 	u32 index_mask;
 	u32 next_plus_upper;
-	u32 reference = 0;
+	u32 reference;
 
 	if (unlikely(object == NULL)) {
 		err("Attempt to acquire reference to non-existent object\n");
@@ -167,8 +174,10 @@ u32 tipc_ref_acquire(void *object, spinlock_t **lock)
 		return 0;
 	}
 
+	/* take a free entry, if available; otherwise initialize a new entry */
+
 	write_lock_bh(&ref_table_lock);
-	if (tipc_ref_table.first_free) {
+	if (likely(tipc_ref_table.first_free != 0)) {
 		index = tipc_ref_table.first_free;
 		entry = &(tipc_ref_table.entries[index]);
 		index_mask = tipc_ref_table.index_mask;
@@ -179,11 +188,23 @@ u32 tipc_ref_acquire(void *object, spinlock_t **lock)
 		reference = (next_plus_upper & ~index_mask) + index;
 		entry->data.reference = reference;
 		entry->object = object;
-		if (lock != NULL)
-			*lock = &entry->lock;
 		spin_unlock_bh(&entry->lock);
+		*lock = &entry->lock;
+	}
+	else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
+		index = tipc_ref_table.init_point++;
+		entry = &(tipc_ref_table.entries[index]);
+		spin_lock_init(&entry->lock);
+		reference = tipc_ref_table.start_mask + index;
+		entry->data.reference = reference;
+		entry->object = object;
+		*lock = &entry->lock;
+	}
+	else {
+		reference = 0;
 	}
 	write_unlock_bh(&ref_table_lock);
+
 	return reference;
 }
 
@@ -200,41 +221,43 @@ void tipc_ref_discard(u32 ref)
 	u32 index;
 	u32 index_mask;
 
-	if (!ref) {
-		err("Attempt to discard reference 0\n");
-		return;
-	}
 	if (unlikely(tipc_ref_table.entries == NULL)) {
 		err("Reference table not found during discard attempt\n");
 		return;
 	}
 
-	write_lock_bh(&ref_table_lock);
 	index_mask = tipc_ref_table.index_mask;
 	index = ref & index_mask;
 	entry = &(tipc_ref_table.entries[index]);
 
+	write_lock_bh(&ref_table_lock);
+
 	if (unlikely(entry->object == NULL)) {
 		err("Attempt to discard reference to non-existent object\n");
 		goto exit;
 	}
-	if (entry->data.reference != ref) {
+	if (unlikely(entry->data.reference != ref)) {
 		err("Attempt to discard non-existent reference\n");
 		goto exit;
 	}
 
-	/* mark entry as unused */
+	/*
+	 * mark entry as unused; increment upper bits of entry's data field
+	 * to invalidate any subsequent references
+	 */
+
 	entry->object = NULL;
+	entry->data.next_plus_upper = (ref & ~index_mask) + (index_mask + 1);
+
+	/* append entry to free entry list */
+
 	if (tipc_ref_table.first_free == 0)
 		tipc_ref_table.first_free = index;
 	else
-		/* next_plus_upper is always XXXX|0--0 for last free entry */
 		tipc_ref_table.entries[tipc_ref_table.last_free].
 			data.next_plus_upper |= index;
 	tipc_ref_table.last_free = index;
 
-	/* increment upper bits of entry to invalidate subsequent references */
-	entry->data.next_plus_upper = (ref & ~index_mask) + (index_mask + 1);
 exit:
 	write_unlock_bh(&ref_table_lock);
 }
@@ -249,10 +272,13 @@ void *tipc_ref_lock(u32 ref)
 		struct reference *r;
 
 		r = &tipc_ref_table.entries[ref & tipc_ref_table.index_mask];
-		spin_lock_bh(&r->lock);
-		if (likely(r->data.reference == ref))
-			return r->object;
-		spin_unlock_bh(&r->lock);
+
+		if (likely(r->data.reference != 0)) {
+			spin_lock_bh(&r->lock);
+			if (likely(r->data.reference == ref))
+				return r->object;
+			spin_unlock_bh(&r->lock);
+		}
 	}
 	return NULL;
 }
@@ -267,11 +293,13 @@ void tipc_ref_unlock(u32 ref)
 		struct reference *r;
 
 		r = &tipc_ref_table.entries[ref & tipc_ref_table.index_mask];
-		if (likely(r->data.reference == ref))
+
+		if (likely((r->data.reference == ref) &&
+			   (r->data.reference != 0)))
 			spin_unlock_bh(&r->lock);
 		else
 			err("tipc_ref_unlock() invoked using "
-			    "obsolete reference\n");
+			    "invalid reference\n");
 	}
 }
 
-- 
1.5.3.2

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