/* 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.
+ *
+ * What?
+ * =====
+ *
+ * A flow classifier holds any number of "rules", each of which specifies
+ * values to match for some fields or subfields and a priority. The primary
+ * design goal for the classifier is that, given a packet, it can as quickly as
+ * possible find the highest-priority rule that matches the packet.
+ *
+ * Each OpenFlow table is implemented as a flow classifier.
+ *
+ *
+ * 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 tracks the highest-priority match that it finds. The
+ * tables are kept in a descending priority order according to the highest
+ * priority rule in each table, which allows lookup to skip over tables that
+ * can't possibly have a higher-priority match than already found.
+ *
+ * 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 tag derived from the
+ * table's mask, so that it is likely that each table has a unique tag.
+ * (Duplicate tags have a performance cost but do not affect
+ * correctness.)
+ *
+ * - 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. In other words, struct cls_partition
+ * associates metadata values with tables that need to be checked with
+ * flows with that specific 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.)
+ *
*
* Thread-safety
* =============
#include "hmap.h"
#include "list.h"
#include "match.h"
+#include "tag.h"
#include "openflow/nicira-ext.h"
#include "openflow/openflow.h"
#include "ovs-thread.h"
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. */
struct ovs_rwlock rwlock OVS_ACQ_AFTER(ofproto_mutex);
};
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
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. */
+ tag_type tags; /* OR of each included flow's cls_table tag. */
+ unsigned int n_refs; /* # of flows that refer to this partition. */
};
void cls_rule_init(struct cls_rule *, const struct match *,
git://git.onelab.eu / sliver-openvswitch.git / blobdiff