sim: A trie data structure specifically to speed up paging lookups.

This change adds a trie data structure which stores an arbitrary pointer type
based on an address and a number of relevant bits. Then lookups can be done
against the trie where the tree is traversed and the first legitimate match
found is returned.

3 files changed, 486 insertions, 0 deletions

diff --git a/src/base/trie.hh b/src/base/trie.hh
new file mode 100644
index 000000000..64b710daf
--- /dev/null
+++ b/src/base/trie.hh
@@ -0,0 +1,358 @@
+/*
+ * Copyright (c) 2012 Google
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#ifndef __BASE_TRIE_HH__
+#define __BASE_TRIE_HH__
+
+#include "base/cprintf.hh"
+#include "base/misc.hh"
+#include "base/types.hh"
+
+// Key has to be an integral type.
+template <class Key, class Value>
+class Trie
+{
+  protected:
+    struct Node
+    {
+        Key key;
+        Key mask;
+
+        bool
+        matches(Key test)
+        {
+            return (test & mask) == key;
+        }
+
+        Value *value;
+
+        Node *parent;
+        Node *kids[2];
+
+        Node(Key _key, Key _mask, Value *_val) :
+            key(_key & _mask), mask(_mask), value(_val),
+            parent(NULL)
+        {
+            kids[0] = NULL;
+            kids[1] = NULL;
+        }
+
+        void
+        clear()
+        {
+            if (kids[1]) {
+                kids[1]->clear();
+                delete kids[1];
+                kids[1] = NULL;
+            }
+            if (kids[0]) {
+                kids[0]->clear();
+                delete kids[0];
+                kids[0] = NULL;
+            }
+        }
+
+        void
+        dump(int level)
+        {
+            for (int i = 1; i < level; i++) {
+                cprintf("|");
+            }
+            if (level == 0)
+                cprintf("Root ");
+            else
+                cprintf("+ ");
+            cprintf("(%p, %p, %#X, %#X, %p)\n", parent, this, key, mask, value);
+            if (kids[0])
+                kids[0]->dump(level + 1);
+            if (kids[1])
+                kids[1]->dump(level + 1);
+        }
+    };
+
+  protected:
+    Node head;
+
+  public:
+    typedef Node *Handle;
+
+    Trie() : head(0, 0, NULL)
+    {}
+
+    static const unsigned MaxBits = sizeof(Key) * 8;
+
+  private:
+    /**
+     * A utility method which checks whether the key being looked up lies
+     * beyond the Node being examined. If so, it returns true and advances the
+     * node being examined.
+     * @param parent The node we're currently "at", which can be updated.
+     * @param kid The node we may want to move to.
+     * @param key The key we're looking for.
+     * @param new_mask The mask to use when matching against the key.
+     * @return Whether the current Node was advanced.
+     */
+    bool
+    goesAfter(Node **parent, Node *kid, Key key, Key new_mask)
+    {
+        if (kid && kid->matches(key) && (kid->mask & new_mask) == kid->mask) {
+            *parent = kid;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * A utility method which extends a mask value one more bit towards the
+     * lsb. This is almost just a signed right shift, except that the shifted
+     * in bits are technically undefined. This is also slightly complicated by
+     * the zero case.
+     * @param orig The original mask to extend.
+     * @return The extended mask.
+     */
+    Key
+    extendMask(Key orig)
+    {
+        // Just in case orig was 0.
+        const Key msb = ULL(1) << (MaxBits - 1);
+        return orig | (orig >> 1) | msb;
+    }
+
+    /**
+     * Method which looks up the Handle corresponding to a particular key. This
+     * is useful if you want to delete the Node corresponding to a key since
+     * the "remove" function takes a Node as its argument.
+     * @param key The key to look up.
+     * @return The first Node matching this key, or NULL if none was found.
+     */
+    Handle
+    lookupHandle(Key key)
+    {
+        Node *node = &head;
+        while (node) {
+            if (node->value)
+                return node;
+
+            if (node->kids[0] && node->kids[0]->matches(key))
+                node = node->kids[0];
+            else if (node->kids[1] && node->kids[1]->matches(key))
+                node = node->kids[1];
+            else
+                node = NULL;
+        }
+
+        return NULL;
+    }
+
+  public:
+    /**
+     * Method which inserts a key/value pair into the trie.
+     * @param key The key which can later be used to look up this value.
+     * @param width How many bits of the key (from msb) should be used.
+     * @param val A pointer to the value to store in the trie.
+     * @return A pointer to the Node which holds this value.
+     */
+    Handle
+    insert(Key key, unsigned width, Value *val)
+    {
+        // Build a mask which masks off all the bits we don't care about.
+        Key new_mask = ~(Key)0;
+        if (width < MaxBits)
+            new_mask <<= (MaxBits - width);
+        // Use it to tidy up the key.
+        key &= new_mask;
+
+        // Walk past all the nodes this new node will be inserted after. They
+        // can be ignored for the purposes of this function.
+        Node *node = &head;
+        while (goesAfter(&node, node->kids[0], key, new_mask) ||
+               goesAfter(&node, node->kids[1], key, new_mask))
+        {}
+        assert(node);
+
+        Key cur_mask = node->mask;
+        // If we're already where the value needs to be...
+        if (cur_mask == new_mask) {
+            assert(!node->value);
+            node->value = val;
+            return node;
+        }
+
+        for (unsigned int i = 0; i < 2; i++) {
+            Node *&kid = node->kids[i];
+            Node *new_node;
+            if (!kid) {
+                // No kid. Add a new one.
+                new_node = new Node(key, new_mask, val);
+                new_node->parent = node;
+                kid = new_node;
+                return new_node;
+            }
+
+            // Walk down the leg until something doesn't match or we run out
+            // of bits.
+            Key last_mask;
+            bool done;
+            do {
+                last_mask = cur_mask;
+                cur_mask = extendMask(cur_mask);
+                done = ((key & cur_mask) != (kid->key & cur_mask)) ||
+                    last_mask == new_mask;
+            } while (!done);
+            cur_mask = last_mask;
+
+            // If this isn't the right leg to go down at all, skip it.
+            if (cur_mask == node->mask)
+                continue;
+
+            // At the point we walked to above, add a new node.
+            new_node = new Node(key, cur_mask, NULL);
+            new_node->parent = node;
+            kid->parent = new_node;
+            new_node->kids[0] = kid;
+            kid = new_node;
+
+            // If we ran out of bits, the value goes right here.
+            if (cur_mask == new_mask) {
+                new_node->value = val;
+                return new_node;
+            }
+
+            // Still more bits to deal with, so add a new node for that path.
+            new_node = new Node(key, new_mask, val);
+            new_node->parent = kid;
+            kid->kids[1] = new_node;
+            return new_node;
+        }
+
+        panic("Reached the end of the Trie insert function!\n");
+        return NULL;
+    }
+
+    /**
+     * Method which looks up the Value corresponding to a particular key.
+     * @param key The key to look up.
+     * @return The first Value matching this key, or NULL if none was found.
+     */
+    Value *
+    lookup(Key key)
+    {
+        Node *node = lookupHandle(key);
+        if (node)
+            return node->value;
+        else
+            return NULL;
+    }
+
+    /**
+     * Method to delete a value from the trie.
+     * @param node A pointer to the Node to remove.
+     * @return The Value pointer from the removed entry.
+     */
+    Value *
+    remove(Handle handle)
+    {
+        Node *node = handle;
+        Value *val = node->value;
+        if (node->kids[1]) {
+            assert(node->value);
+            node->value = NULL;
+            return val;
+        }
+        if (!node->parent)
+            panic("Trie: Can't remove root node.\n");
+
+        Node *parent = node->parent;
+
+        // If there's a kid, fix up it's parent pointer.
+        if (node->kids[0])
+            node->kids[0]->parent = parent;
+        // Figure out which kid we are, and update our parent's pointers.
+        if (parent->kids[0] == node)
+            parent->kids[0] = node->kids[0];
+        else if (parent->kids[1] == node)
+            parent->kids[1] = node->kids[0];
+        else
+            panic("Trie: Inconsistent parent/kid relationship.\n");
+        // Make sure if the parent only has one kid, it's kid[0].
+        if (parent->kids[1] && !parent->kids[0]) {
+            parent->kids[0] = parent->kids[1];
+            parent->kids[1] = NULL;
+        }
+
+        // If the parent has less than two kids and no cargo and isn't the
+        // root, delete it too.
+        if (!parent->kids[1] && !parent->value && parent->parent)
+            remove(parent);
+        delete node;
+        return val;
+    }
+
+    /**
+     * Method to lookup a value from the trie and then delete it.
+     * @param key The key to look up and then remove.
+     * @return The Value pointer from the removed entry, if any.
+     */
+    Value *
+    remove(Key key)
+    {
+        Handle handle = lookupHandle(key);
+        if (!handle)
+            return NULL;
+        return remove(handle);
+    }
+
+    /**
+     * A method which removes all key/value pairs from the trie. This is more
+     * efficient than trying to remove elements individually.
+     */
+    void
+    clear()
+    {
+        head.clear();
+    }
+
+    /**
+     * A debugging method which prints the contents of this trie.
+     * @param title An identifying title to put in the dump header.
+     */
+    void
+    dump(const char *title)
+    {
+        cprintf("**************************************************\n");
+        cprintf("*** Start of Trie: %s\n", title);
+        cprintf("*** (parent, me, key, mask, value pointer)\n");
+        cprintf("**************************************************\n");
+        head.dump(0);
+    }
+};
+
+#endif
diff --git a/src/unittest/SConscript b/src/unittest/SConscript
index 606bffd05..3ceae23b5 100644
--- a/src/unittest/SConscript
+++ b/src/unittest/SConscript
@@ -48,6 +48,7 @@ UnitTest('rangemaptest', 'rangemaptest.cc')
 UnitTest('rangemultimaptest', 'rangemultimaptest.cc')
 UnitTest('refcnttest', 'refcnttest.cc')
 UnitTest('strnumtest', 'strnumtest.cc')
+UnitTest('trietest', 'trietest.cc')
 
 stattest_py = PySource('m5', 'stattestmain.py', skip_lib=True)
 stattest_swig = SwigSource('m5.internal', 'stattest.i', skip_lib=True)
diff --git a/src/unittest/trietest.cc b/src/unittest/trietest.cc
new file mode 100644
index 000000000..ed8a772fa
--- /dev/null
+++ b/src/unittest/trietest.cc
@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2012 Google
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#include <cassert>
+#include <iostream>
+
+#include "base/cprintf.hh"
+#include "base/trie.hh"
+#include "base/types.hh"
+#include "unittest/unittest.hh"
+
+using UnitTest::setCase;
+
+typedef Trie<Addr, uint32_t> TestTrie;
+
+int
+main()
+{
+    // Create an empty Ptr and verify it's data pointer is NULL.
+    setCase("An empty trie.");
+    TestTrie trie1;
+    trie1.dump("Empty");
+    cprintf("\n\n");
+
+    setCase("A single entry.");
+    trie1.insert(0x0123456789abcdef, 40, (uint32_t *)(uintptr_t)(1));
+    trie1.dump("One entry");
+    cprintf("\n\n");
+
+    setCase("Two entries, one on the way to the other.");
+    TestTrie trie2;
+    trie2.insert(0x0123456789abcdef, 40, (uint32_t *)(uintptr_t)(1));
+    trie2.insert(0x0123456789abcdef, 36, (uint32_t *)(uintptr_t)(2));
+    trie2.dump("Two entries inline v1");
+    cprintf("\n\n");
+
+    TestTrie trie3;
+    trie3.insert(0x0123456789abcdef, 36, (uint32_t *)(uintptr_t)(2));
+    trie3.insert(0x0123456789abcdef, 40, (uint32_t *)(uintptr_t)(1));
+    trie3.dump("Two entries inline v2");
+    cprintf("\n\n");
+
+    setCase("Two entries on different paths.");
+    TestTrie trie4;
+    trie4.insert(0x0123456789abcdef, 40, (uint32_t *)(uintptr_t)(2));
+    trie4.insert(0x0123456776543210, 40, (uint32_t *)(uintptr_t)(1));
+    trie4.dump("Two split entries");
+    cprintf("\n\n");
+
+    setCase("Skipping past an entry but not two.");
+    TestTrie trie5;
+    trie5.insert(0x0123456789000000, 40, (uint32_t *)(uintptr_t)(4));
+    trie5.insert(0x0123000000000000, 40, (uint32_t *)(uintptr_t)(1));
+    trie5.insert(0x0123456780000000, 40, (uint32_t *)(uintptr_t)(3));
+    trie5.insert(0x0123456700000000, 40, (uint32_t *)(uintptr_t)(2));
+    trie5.dump("Complex insertion");
+    cprintf("\n\n");
+
+    setCase("Looking things up.");
+    EXPECT_EQ((uintptr_t)trie5.lookup(0x0123000000000000), 1);
+    EXPECT_EQ((uintptr_t)trie5.lookup(0x0123456700000000), 2);
+    EXPECT_EQ((uintptr_t)trie5.lookup(0x0123456780000000), 3);
+    EXPECT_EQ((uintptr_t)trie5.lookup(0x0123456789000000), 4);
+
+    setCase("Removing entries.");
+    TestTrie trie6;
+    TestTrie::Handle node1, node2;
+    trie6.insert(0x0123456789000000, 40, (uint32_t *)(uintptr_t)(4));
+    trie6.insert(0x0123000000000000, 40, (uint32_t *)(uintptr_t)(1));
+    trie6.insert(0x0123456780000000, 40, (uint32_t *)(uintptr_t)(3));
+    node1 = trie6.insert(0x0123456700000000, 40, (uint32_t *)(uintptr_t)(2));
+    node2 = trie6.insert(0x0123456700000000, 32, (uint32_t *)(uintptr_t)(10));
+    trie6.dump("Fill before removal");
+    cprintf("\n\n");
+
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123000000000000), 1);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456700000000), 10);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456780000000), 10);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456789000000), 10);
+
+    trie6.remove(node2);
+    trie6.dump("One node removed");
+    cprintf("\n\n");
+
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123000000000000), 1);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456700000000), 2);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456780000000), 3);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456789000000), 4);
+
+    trie6.remove(node1);
+    trie6.dump("Two nodes removed");
+    cprintf("\n\n");
+
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123000000000000), 1);
+    EXPECT_EQ(trie6.lookup(0x0123456700000000), NULL);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456780000000), 3);
+    EXPECT_EQ((uintptr_t)trie6.lookup(0x0123456789000000), 4);
+
+    return UnitTest::printResults();
+}