[ovs-dev] [partition v2 3/3] classifier: Speed up lookup when metadata partitions the flow table.

Ben Pfaff blp at nicira.com
Thu Jun 27 22:30:14 UTC 2013


We have a controller that puts many rules with different metadata values
into the flow table, where metadata is used (by "resubmit"s) to distinguish
stages in a pipeline.  Thus, any given flow only needs to be hashed into
classifier "cls_table"s that contain a match for the flow's metadata value.
This commit optimizes the classifier lookup by (probabilistically) skipping
the "cls_table"s that can't possibly match.

(The "metadata" referred to here is the OpenFlow 1.1+ "metadata" field,
which is a 64-bit field similar in purpose to the "registers" defined by
Open vSwitch.)

This speeds up flow setup performance with the controller in question by
about 19%.

Bug #14282.
Signed-off-by: Ben Pfaff <blp at nicira.com>
---
 lib/classifier.c |  116 +++++++++++++++++++++++++++++++++++++++++++++++++----
 lib/classifier.h |   74 +++++++++++++++++++++++++++++++---
 lib/flow.h       |   27 ++++++++++++
 lib/tag.h        |    8 +++-
 4 files changed, 209 insertions(+), 16 deletions(-)

diff --git a/lib/classifier.c b/lib/classifier.c
index bd202f6..0af6e17 100644
--- a/lib/classifier.c
+++ b/lib/classifier.c
@@ -41,7 +41,7 @@ static void update_tables_after_removal(struct classifier *,
                                         unsigned int del_priority);
 
 static struct cls_rule *find_match(const struct cls_table *,
-                                   const struct flow *);
+                                   const struct flow *, tag_type tags);
 static struct cls_rule *find_equal(struct cls_table *,
                                    const struct miniflow *, uint32_t hash);
 static struct cls_rule *insert_rule(struct classifier *,
@@ -143,6 +143,7 @@ classifier_init(struct classifier *cls)
     cls->n_rules = 0;
     hmap_init(&cls->tables);
     list_init(&cls->tables_priority);
+    hmap_init(&cls->partitions);
 }
 
 /* Destroys 'cls'.  Rules within 'cls', if any, are not freed; this is the
@@ -151,12 +152,20 @@ void
 classifier_destroy(struct classifier *cls)
 {
     if (cls) {
+        struct cls_table *partition, *next_partition;
         struct cls_table *table, *next_table;
 
         HMAP_FOR_EACH_SAFE (table, next_table, hmap_node, &cls->tables) {
             destroy_table(cls, table);
         }
         hmap_destroy(&cls->tables);
+
+        HMAP_FOR_EACH_SAFE (partition, next_partition, hmap_node,
+                            &cls->partitions) {
+            hmap_remove(&cls->partitions, &partition->hmap_node);
+            free(partition);
+        }
+        hmap_destroy(&cls->partitions);
     }
 }
 
@@ -174,6 +183,46 @@ classifier_count(const struct classifier *cls)
     return cls->n_rules;
 }
 
+static uint32_t
+hash_metadata(ovs_be64 metadata_)
+{
+    uint64_t metadata = (OVS_FORCE uint64_t) metadata_;
+    return hash_2words(metadata, metadata >> 32);
+}
+
+static struct cls_partition *
+find_partition(const struct classifier *cls, ovs_be64 metadata, uint32_t hash)
+{
+    struct cls_partition *partition;
+
+    HMAP_FOR_EACH_IN_BUCKET (partition, hmap_node, hash, &cls->partitions) {
+        if (partition->metadata == metadata) {
+            return partition;
+        }
+    }
+
+    return NULL;
+}
+
+static struct cls_partition *
+create_partition(struct classifier *cls, struct cls_table *table,
+                 ovs_be64 metadata)
+{
+    uint32_t hash = hash_metadata(metadata);
+    struct cls_partition *partition = find_partition(cls, metadata, hash);
+    if (partition) {
+        partition->n_refs++;
+        partition->tags |= table->tag;
+    } else {
+        partition = xmalloc(sizeof *partition);
+        partition->n_refs = 1;
+        partition->tags = table->tag;
+        partition->metadata = metadata;
+        hmap_insert(&cls->partitions, &partition->hmap_node, hash);
+    }
+    return partition;
+}
+
 /* Inserts 'rule' into 'cls'.  Until 'rule' is removed from 'cls', the caller
  * must not modify or free it.
  *
@@ -200,8 +249,17 @@ classifier_replace(struct classifier *cls, struct cls_rule *rule)
 
     old_rule = insert_rule(cls, table, rule);
     if (!old_rule) {
+        if (minimask_get_metadata_mask(&rule->match.mask) == OVS_BE64_MAX) {
+            ovs_be64 metadata = miniflow_get_metadata(&rule->match.flow);
+            rule->partition = create_partition(cls, table, metadata);
+        } else {
+            rule->partition = NULL;
+        }
+
         table->n_table_rules++;
         cls->n_rules++;
+    } else {
+        rule->partition = old_rule->partition;
     }
     return old_rule;
 }
@@ -225,6 +283,7 @@ classifier_insert(struct classifier *cls, struct cls_rule *rule)
 void
 classifier_remove(struct classifier *cls, struct cls_rule *rule)
 {
+    struct cls_partition *partition;
     struct cls_rule *head;
     struct cls_table *table;
 
@@ -242,6 +301,12 @@ classifier_remove(struct classifier *cls, struct cls_rule *rule)
         hmap_replace(&table->rules, &rule->hmap_node, &next->hmap_node);
     }
 
+    partition = rule->partition;
+    if (partition && --partition->n_refs == 0) {
+        hmap_remove(&cls->partitions, &partition->hmap_node);
+        free(partition);
+    }
+
     if (--table->n_table_rules == 0) {
         destroy_table(cls, table);
     } else {
@@ -262,12 +327,38 @@ struct cls_rule *
 classifier_lookup(const struct classifier *cls, const struct flow *flow,
                   struct flow_wildcards *wc)
 {
+    const struct cls_partition *partition;
     struct cls_table *table;
     struct cls_rule *best;
+    tag_type tags;
+
+    /* Determine 'tags' such that, if 'table->tag' doesn't intersect them, then
+     * 'flow' cannot possibly match in 'table':
+     *
+     *     - If flow->metadata maps to a given 'partition', then we can use
+     *       'tags' for 'partition->tags'.
+     *
+     *     - If flow->metadata has no partition, then no rule in 'cls' has an
+     *       exact-match for flow->metadata.  That means that we don't need to
+     *       search any table that includes flow->metadata in its mask.
+     *
+     * In either case, we always need to search any cls_tables that do not
+     * include flow->metadata in its mask.  One way to do that would be to
+     * check the "cls_table"s explicitly for that, but that would require an
+     * extra branch per table.  Instead, we mark such a cls_table's 'tags' as
+     * TAG_ALL and make sure that 'tags' is never empty.  This means that
+     * 'tags' always intersects such a cls_table's 'tags', so we don't need a
+     * special case.
+     */
+    partition = (hmap_is_empty(&cls->partitions)
+                 ? NULL
+                 : find_partition(cls, flow->metadata,
+                                  hash_metadata(flow->metadata)));
+    tags = partition ? partition->tags : TAG_ARBITRARY;
 
     best = NULL;
     LIST_FOR_EACH (table, list_node, &cls->tables_priority) {
-        struct cls_rule *rule = find_match(table, flow);
+        struct cls_rule *rule = find_match(table, flow, tags);
 
         if (wc) {
             flow_wildcards_fold_minimask(wc, &table->mask);
@@ -280,7 +371,7 @@ classifier_lookup(const struct classifier *cls, const struct flow *flow,
                      * can not find anything better. */
                     return best;
                 }
-                rule = find_match(table, flow);
+                rule = find_match(table, flow, tags);
                 if (wc) {
                     flow_wildcards_fold_minimask(wc, &table->mask);
                 }
@@ -536,6 +627,7 @@ find_table(const struct classifier *cls, const struct minimask *mask)
 static struct cls_table *
 insert_table(struct classifier *cls, const struct minimask *mask)
 {
+    uint32_t hash = minimask_hash(mask, 0);
     struct cls_table *table;
 
     table = xzalloc(sizeof *table);
@@ -543,6 +635,9 @@ insert_table(struct classifier *cls, const struct minimask *mask)
     minimask_clone(&table->mask, mask);
     hmap_insert(&cls->tables, &table->hmap_node, minimask_hash(mask, 0));
     list_push_back(&cls->tables_priority, &table->list_node);
+    table->tag = (minimask_get_metadata_mask(mask) == OVS_BE64_MAX
+                  ? tag_create_deterministic(hash)
+                  : TAG_ALL);
 
     return table;
 }
@@ -648,14 +743,17 @@ update_tables_after_removal(struct classifier *cls, struct cls_table *table,
 }
 
 static struct cls_rule *
-find_match(const struct cls_table *table, const struct flow *flow)
+find_match(const struct cls_table *table, const struct flow *flow,
+           tag_type tags)
 {
-    uint32_t hash = flow_hash_in_minimask(flow, &table->mask, 0);
-    struct cls_rule *rule;
+    if (tag_intersects(tags, table->tag)) {
+        uint32_t hash = flow_hash_in_minimask(flow, &table->mask, 0);
+        struct cls_rule *rule;
 
-    HMAP_FOR_EACH_WITH_HASH (rule, hmap_node, hash, &table->rules) {
-        if (minimatch_matches_flow(&rule->match, flow)) {
-            return rule;
+        HMAP_FOR_EACH_WITH_HASH (rule, hmap_node, hash, &table->rules) {
+            if (minimatch_matches_flow(&rule->match, flow)) {
+                return rule;
+            }
         }
     }
 
diff --git a/lib/classifier.h b/lib/classifier.h
index fdc3af7..07a2929 100644
--- a/lib/classifier.h
+++ b/lib/classifier.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009, 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,17 +19,66 @@
 
 /* Flow classifier.
  *
- * A classifier is a "struct classifier",
- *      a hash map from a set of wildcards to a "struct cls_table",
- *              a hash map from fixed field values to "struct cls_rule",
- *                      which can contain a list of otherwise identical rules
- *                      with lower priorities.
+ * Basic Design
+ * ============
+ *
+ * Suppose that all the rules in a classifier had the same form.  For example,
+ * suppose that they all matched on the source and destination Ethernet address
+ * and wildcarded all the other fields.  Then the obvious way to implement a
+ * classifier would be a hash table on the source and destination Ethernet
+ * addresses.  If new classification rules came along with a different form,
+ * you could add a second hash table that hashed on the fields matched in those
+ * rules.  With two hash tables, you look up a given flow in each hash table.
+ * If there are no matches, the classifier didn't contain a match; if you find
+ * a match in one of them, that's the result; if you find a match in both of
+ * them, then the result is the rule with the higher priority.
+ *
+ * This is how the classifier works.  In a "struct classifier", each form of
+ * "struct cls_rule" present (based on its ->match.mask) goes into a separate
+ * "struct cls_table".  A lookup does a hash lookup in every "struct cls_table"
+ * in the classifier and returns the highest-priority match that it finds.
+ *
+ * One detail: a classifier can contain multiple rules that are identical other
+ * than their priority.  When this happens, only the highest priority rule out
+ * of a group of otherwise identical rules is stored directly in the "struct
+ * cls_table", with the other almost-identical rules chained off a linked list
+ * inside that highest-priority rule.
+ *
+ *
+ * Partitioning
+ * ============
+ *
+ * Suppose that a given classifier is being used to handle multiple stages in a
+ * pipeline using "resubmit", with metadata (that is, the OpenFlow 1.1+ field
+ * named "metadata") distinguishing between the different stages.  For example,
+ * metadata value 1 might identify ingress rules, metadata value 2 might
+ * identify ACLs, and metadata value 3 might identify egress rules.  Such a
+ * classifier is essentially partitioned into multiple sub-classifiers on the
+ * basis of the metadata value.
+ *
+ * The classifier has a special optimization to speed up matching in this
+ * scenario:
+ *
+ *     - Each cls_table that matches on metadata gets a random tag (see tag.h).
+ *
+ *     - For each metadata value matched by any cls_rule, the classifier
+ *       constructs a "struct cls_partition" indexed by the metadata value.
+ *       The cls_partition has a 'tags' member whose value is the bitwise-OR of
+ *       the tags of each cls_table that contains any rule that matches on the
+ *       cls_partition's metadata value.
+ *
+ * Thus, a flow lookup can start by looking up the partition associated with
+ * the flow's metadata, and then skip over any cls_table whose 'tag' does not
+ * intersect the partition's 'tags'.  (The flow must also be looked up in any
+ * cls_table that doesn't match on metadata.  We handle that by giving any such
+ * cls_table TAG_ALL as its 'tags' so that it matches any tag.)
  */
 
 #include "flow.h"
 #include "hmap.h"
 #include "list.h"
 #include "match.h"
+#include "tag.h"
 #include "openflow/nicira-ext.h"
 #include "openflow/openflow.h"
 
@@ -42,6 +91,7 @@ struct classifier {
     int n_rules;                /* Total number of rules. */
     struct hmap tables;         /* Contains "struct cls_table"s.  */
     struct list tables_priority; /* Tables in descending priority order */
+    struct hmap partitions;     /* Contains "struct cls_partition"s. */
 };
 
 /* A set of rules that all have the same fields wildcarded. */
@@ -53,6 +103,7 @@ struct cls_table {
     int n_table_rules;          /* Number of rules, including duplicates. */
     unsigned int max_priority;  /* Max priority of any rule in the table. */
     unsigned int max_count;     /* Count of max_priority rules. */
+    tag_type tag;               /* Tag generated from mask for partitioning. */
 };
 
 /* Returns true if 'table' is a "catch-all" table that will match every
@@ -69,6 +120,17 @@ struct cls_rule {
     struct list list;           /* List of identical, lower-priority rules. */
     struct minimatch match;     /* Matching rule. */
     unsigned int priority;      /* Larger numbers are higher priorities. */
+    struct cls_partition *partition;
+};
+
+/* Associates a metadata value (that is, a value of the OpenFlow 1.1+ metadata
+ * field) with tags for the "cls_table"s that contain rules that match that
+ * metadata value.  */
+struct cls_partition {
+    struct hmap_node hmap_node; /* In struct classifier's 'partitions' hmap. */
+    ovs_be64 metadata;          /* metadata value for this partition. */
+    unsigned int n_refs;        /* # of flows that refer to this partition. */
+    tag_type tags;              /* OR of each included flow's cls_table tag. */
 };
 
 void cls_rule_init(struct cls_rule *, const struct match *,
diff --git a/lib/flow.h b/lib/flow.h
index 2c027ed..89c52b1 100644
--- a/lib/flow.h
+++ b/lib/flow.h
@@ -21,6 +21,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <string.h>
+#include "byte-order.h"
 #include "openflow/nicira-ext.h"
 #include "openflow/openflow.h"
 #include "hash.h"
@@ -327,6 +328,7 @@ void miniflow_expand(const struct miniflow *, struct flow *);
 
 uint32_t miniflow_get(const struct miniflow *, unsigned int u32_ofs);
 uint16_t miniflow_get_vid(const struct miniflow *);
+static inline ovs_be64 miniflow_get_metadata(const struct miniflow *);
 
 bool miniflow_equal(const struct miniflow *a, const struct miniflow *b);
 bool miniflow_equal_in_minimask(const struct miniflow *a,
@@ -359,11 +361,36 @@ void minimask_expand(const struct minimask *, struct flow_wildcards *);
 
 uint32_t minimask_get(const struct minimask *, unsigned int u32_ofs);
 uint16_t minimask_get_vid_mask(const struct minimask *);
+static inline ovs_be64 minimask_get_metadata_mask(const struct minimask *);
 
 bool minimask_equal(const struct minimask *a, const struct minimask *b);
 uint32_t minimask_hash(const struct minimask *, uint32_t basis);
 
 bool minimask_has_extra(const struct minimask *, const struct minimask *);
 bool minimask_is_catchall(const struct minimask *);
+
+/* Returns the value of the OpenFlow 1.1+ "metadata" field in 'flow'. */
+static inline ovs_be64
+miniflow_get_metadata(const struct miniflow *flow)
+{
+    enum { MD_OFS = offsetof(struct flow, metadata) };
+    BUILD_ASSERT_DECL(MD_OFS % sizeof(uint32_t) == 0);
+    ovs_be32 hi = (OVS_FORCE ovs_be32) miniflow_get(flow, MD_OFS / 4);
+    ovs_be32 lo = (OVS_FORCE ovs_be32) miniflow_get(flow, MD_OFS / 4 + 1);
+
+    return htonll(((uint64_t) ntohl(hi) << 32) | ntohl(lo));
+}
+
+/* Returns the mask for the OpenFlow 1.1+ "metadata" field in 'mask'.
+ *
+ * The return value is all-1-bits if 'mask' matches on the whole value of the
+ * metadata field, all-0-bits if 'mask' entirely wildcards the metadata field,
+ * or some other value if the metadata field is partially matched, partially
+ * wildcarded. */
+static inline ovs_be64
+minimask_get_metadata_mask(const struct minimask *mask)
+{
+    return miniflow_get_metadata(&mask->masks);
+}
 
 #endif /* flow.h */
diff --git a/lib/tag.h b/lib/tag.h
index 9d6b4aa..6fec24b 100644
--- a/lib/tag.h
+++ b/lib/tag.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2008, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -68,6 +68,12 @@
 /* Represents a tag, or the combination of 0 or more tags. */
 typedef uint32_t tag_type;
 
+/* A 'tag_type' value that intersects every tag. */
+#define TAG_ALL UINT32_MAX
+
+/* An arbitrary tag. */
+#define TAG_ARBITRARY UINT32_C(3)
+
 tag_type tag_create_random(void);
 tag_type tag_create_deterministic(uint32_t seed);
 static inline bool tag_intersects(tag_type, tag_type);
-- 
1.7.2.5




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