[ovs-dev,v12,4/5] dpif-netdev: Refactor generic implementation
diff mbox series

Message ID 20190717130033.25114-5-harry.van.haaren@intel.com
State Superseded
Headers show
Series
  • dpcls func ptrs & optimizations
Related show

Commit Message

Harry van Haaren July 17, 2019, 1 p.m. UTC
This commit refactors the generic implementation. The
goal of this refactor is to simplify the code to enable
"specialization" of the functions at compile time.

Given compile-time optimizations, the compiler is able
to unroll loops, and create optimized code sequences due
to compile time knowledge of loop-trip counts.

In order to enable these compiler optimizations, we must
refactor the code to pass the loop-trip counts to functions
as compile time constants.

This patch allows the number of miniflow-bits set per "unit"
in the miniflow to be passed around as a function argument.

Note that this patch does NOT yet take advantage of doing so,
this is only a refactor to enable it in the next patches.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Tested-by: Malvika Gupta <malvika.gupta@arm.com>

---

v12:
- Fix Caps and . (Ilya)
- Fixed typos (Ilya)
- Added mf_bits and mf_masks in this patch (Ilya)
- Fixed rebase conflicts

v11:
- Rebased to previous changes
- Fix typo in commit message (Ian)
- Fix variable declaration spacing (Ian)
- Remove function names from comments (Ian)
- Replace magic 8 with sizeof(uint64_t) (Ian)
- Captialize and end comments with a stop. (Ian/Ilya)
- Add build time assert to validate FLOWMAP_UNITS (Ilya)
- Add note on ALWAYS_INLINE operation
- Add space after ULLONG_FOR_EACH_1 (Ilya)
- Use hash_add_words64() instead of rolling own loop (Ilya)
    Note that hash_words64_inline() calls hash_finish() with an
    fixed value, so it was not the right hash function for this
    usage. Used hash_add_words64() and manual hash_finish() to
    re-use as much of hashing code as we can.

v10:
- Rebase updates from previous patches
- Fix whitespace indentation of func params
- Removed restrict keyword, Windows CI failing when it is used (Ian)
- Fix integer 0 used to set NULL pointer (Ilya)
- Postpone free() call on cls->blocks_scratch (Ilya)
- Fix indentation of a function

v9:
- Use count_1bits in favour of __builtin_popcount (Ilya)
- Use ALWAYS_INLINE instead of __attribute__ synatx (Ilya)

v8:
- Rework block_cache and mf_masks to avoid variable-lenght array
  due to compiler issues. Provisioning for worst case is not a
  good solution due to magnitue of over-provisioning required.
- Rework netdev_flatten function removing unused parameter
---
 lib/dpif-netdev-lookup-generic.c | 205 ++++++++++++++++++++++++++-----
 lib/dpif-netdev-private.h        |  14 ++-
 lib/dpif-netdev.c                |  77 +++++++++++-
 3 files changed, 261 insertions(+), 35 deletions(-)

Patch
diff mbox series

diff --git a/lib/dpif-netdev-lookup-generic.c b/lib/dpif-netdev-lookup-generic.c
index 8064911b3..b38adc2d5 100644
--- a/lib/dpif-netdev-lookup-generic.c
+++ b/lib/dpif-netdev-lookup-generic.c
@@ -30,58 +30,186 @@ 
 #include "packets.h"
 #include "pvector.h"
 
-/* Returns a hash value for the bits of 'key' where there are 1-bits in
- * 'mask'. */
-static inline uint32_t
-netdev_flow_key_hash_in_mask(const struct netdev_flow_key *key,
-                             const struct netdev_flow_key *mask)
+VLOG_DEFINE_THIS_MODULE(dpif_lookup_generic);
+
+/* Lookup functions below depends on the internal structure of flowmap. */
+BUILD_ASSERT_DECL(FLOWMAP_UNITS == 2);
+
+/* Given a packet, table and mf_masks, this function iterates over each bit
+ * set in the subtable, and calculates the appropriate metadata to store in the
+ * blocks_scratch[].
+ *
+ * The results of the blocks_scratch[] can be used for hashing, and later for
+ * verification of if a rule matches the given packet.
+ */
+static inline void
+netdev_flow_key_flatten_unit(const uint64_t *pkt_blocks,
+                             const uint64_t *tbl_blocks,
+                             const uint64_t *mf_masks,
+                             uint64_t *blocks_scratch,
+                             const uint64_t pkt_mf_bits,
+                             const uint32_t count)
 {
-    const uint64_t *p = miniflow_get_values(&mask->mf);
-    uint32_t hash = 0;
-    uint64_t value;
+    uint32_t i;
+
+    for (i = 0; i < count; i++) {
+        uint64_t mf_mask = mf_masks[i];
+        /* Calculate the block index for the packet metadata. */
+        uint64_t idx_bits = mf_mask & pkt_mf_bits;
+        const uint32_t pkt_idx = count_1bits(idx_bits);
+
+        /* Check if the packet has the subtable miniflow bit set. If yes, the
+         * block at the above pkt_idx will be stored, otherwise it is masked
+         * out to be zero.
+         */
+        uint64_t pkt_has_mf_bit = (mf_mask + 1) & pkt_mf_bits;
+        uint64_t no_bit = ((!pkt_has_mf_bit) > 0) - 1;
 
-    NETDEV_FLOW_KEY_FOR_EACH_IN_FLOWMAP (value, key, mask->mf.map) {
-        hash = hash_add64(hash, value & *p);
-        p++;
+        /* Mask packet block by table block, and mask to zero if packet
+         * doesn't actually contain this block of metadata.
+         */
+        blocks_scratch[i] = pkt_blocks[pkt_idx] & tbl_blocks[i] & no_bit;
     }
+}
+
+/* This function takes a packet, and subtable and writes an array of uint64_t
+ * blocks. The blocks contain the metadata that the subtable matches on, in
+ * the same order as the subtable, allowing linear iteration over the blocks.
+ *
+ * To calculate the blocks contents, the netdev_flow_key_flatten_unit function
+ * is called twice, once for each "unit" of the miniflow. This call can be
+ * inlined by the compiler for performance.
+ *
+ * Note that the u0_count and u1_count variables can be compile-time constants,
+ * allowing the loop in the inlined flatten_unit() function to be compile-time
+ * unrolled, or possibly removed totally by unrolling by the loop iterations.
+ * The compile time optimizations enabled by this design improves performance.
+ */
+static inline void
+netdev_flow_key_flatten(const struct netdev_flow_key *key,
+                        const struct netdev_flow_key *mask,
+                        const uint64_t *mf_masks,
+                        uint64_t *blocks_scratch,
+                        const uint32_t u0_count,
+                        const uint32_t u1_count)
+{
+    /* Load mask from subtable, mask with packet mf, popcount to get idx. */
+    const uint64_t *pkt_blocks = miniflow_get_values(&key->mf);
+    const uint64_t *tbl_blocks = miniflow_get_values(&mask->mf);
 
-    return hash_finish(hash, (p - miniflow_get_values(&mask->mf)) * 8);
+    /* Packet miniflow bits to be masked by pre-calculated mf_masks. */
+    const uint64_t pkt_bits_u0 = key->mf.map.bits[0];
+    const uint32_t pkt_bits_u0_pop = count_1bits(pkt_bits_u0);
+    const uint64_t pkt_bits_u1 = key->mf.map.bits[1];
+
+    /* Unit 0 flattening */
+    netdev_flow_key_flatten_unit(&pkt_blocks[0],
+                                 &tbl_blocks[0],
+                                 &mf_masks[0],
+                                 &blocks_scratch[0],
+                                 pkt_bits_u0,
+                                 u0_count);
+
+    /* Unit 1 flattening:
+     * Move the pointers forward in the arrays based on u0 offsets, NOTE:
+     * 1) pkt blocks indexed by actual popcount of u0, which is NOT always
+     *    the same as the amount of bits set in the subtable.
+     * 2) mf_masks, tbl_block and blocks_scratch are all "flat" arrays, so
+     *    the index is always u0_count.
+     */
+    netdev_flow_key_flatten_unit(&pkt_blocks[pkt_bits_u0_pop],
+                                 &tbl_blocks[u0_count],
+                                 &mf_masks[u0_count],
+                                 &blocks_scratch[u0_count],
+                                 pkt_bits_u1,
+                                 u1_count);
 }
 
-uint32_t
-dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
-                              uint32_t keys_map,
-                              const struct netdev_flow_key *keys[],
-                              struct dpcls_rule **rules)
+/* Compares a rule and the blocks representing a key, returns 1 on a match. */
+static inline uint64_t
+netdev_rule_matches_key(const struct dpcls_rule *rule,
+                        const uint32_t mf_bits_total,
+                        const uint64_t *blocks_scratch)
 {
-    int i;
-    uint32_t found_map;
+    const uint64_t *keyp = miniflow_get_values(&rule->flow.mf);
+    const uint64_t *maskp = miniflow_get_values(&rule->mask->mf);
+    uint64_t not_match = 0;
+
+    for (int i = 0; i < mf_bits_total; i++) {
+        not_match |= (blocks_scratch[i] & maskp[i]) != keyp[i];
+    }
 
-    /* Compute hashes for the remaining keys.  Each search-key is
-     * masked with the subtable's mask to avoid hashing the wildcarded
-     * bits. */
+    /* Invert result to show match as 1. */
+    return !not_match;
+}
+
+/* Const prop version of the function: note that mf bits total and u0 are
+ * explicitly passed in here, while they're also available at runtime from the
+ * subtable pointer. By making them compile time, we enable the compiler to
+ * unroll loops and flatten out code-sequences based on the knowledge of the
+ * mf_bits_* compile time values. This results in improved performance.
+ *
+ * Note: this function is marked with ALWAYS_INLINE to ensure the compiler
+ * inlines the below code, and then uses the compile time constants to make
+ * specialized versions of the runtime code. Without ALWAYS_INLINE, the
+ * compiler might decide to not inline, and performance will suffer.
+ */
+static inline uint32_t ALWAYS_INLINE
+lookup_generic_impl(struct dpcls_subtable *subtable,
+                    uint64_t *blocks_scratch,
+                    uint32_t keys_map,
+                    const struct netdev_flow_key *keys[],
+                    struct dpcls_rule **rules,
+                    const uint32_t bit_count_u0,
+                    const uint32_t bit_count_u1)
+{
+    const uint32_t n_pkts = count_1bits(keys_map);
+    ovs_assert(NETDEV_MAX_BURST >= n_pkts);
     uint32_t hashes[NETDEV_MAX_BURST];
+
+    const uint32_t bit_count_total = bit_count_u0 + bit_count_u1;
+    uint64_t *mf_masks = subtable->mf_masks;
+    int i;
+
+    /* Flatten the packet metadata into the blocks_scratch[] using subtable. */
+    ULLONG_FOR_EACH_1 (i, keys_map) {
+            netdev_flow_key_flatten(keys[i],
+                                    &subtable->mask,
+                                    mf_masks,
+                                    &blocks_scratch[i * bit_count_total],
+                                    bit_count_u0,
+                                    bit_count_u1);
+    }
+
+    /* Hash the now linearized blocks of packet metadata. */
     ULLONG_FOR_EACH_1 (i, keys_map) {
-        hashes[i] = netdev_flow_key_hash_in_mask(keys[i], &subtable->mask);
+        uint64_t *block_ptr = &blocks_scratch[i * bit_count_total];
+        uint32_t hash = hash_add_words64(0, block_ptr, bit_count_total);
+        hashes[i] = hash_finish(hash, bit_count_total * 8);
     }
 
-    /* Lookup. */
+    /* Lookup: this returns a bitmask of packets where the hash table had
+     * an entry for the given hash key. Presence of a hash key does not
+     * guarantee matching the key, as there can be hash collisions.
+     */
+    uint32_t found_map;
     const struct cmap_node *nodes[NETDEV_MAX_BURST];
+
     found_map = cmap_find_batch(&subtable->rules, keys_map, hashes, nodes);
 
-    /* Check results.  When the i-th bit of found_map is set, it means
-     * that a set of nodes with a matching hash value was found for the
-     * i-th search-key.  Due to possible hash collisions we need to check
-     * which of the found rules, if any, really matches our masked
-     * search-key. */
+    /* Verify that packet actually matched rule. If not found, a hash
+     * collision has taken place, so continue searching with the next node.
+     */
     ULLONG_FOR_EACH_1 (i, found_map) {
         struct dpcls_rule *rule;
 
         CMAP_NODE_FOR_EACH (rule, cmap_node, nodes[i]) {
-            if (OVS_LIKELY(dpcls_rule_matches_key(rule, keys[i]))) {
+            const uint32_t cidx = i * bit_count_total;
+            uint32_t match = netdev_rule_matches_key(rule, bit_count_total,
+                                                     &blocks_scratch[cidx]);
+
+            if (OVS_LIKELY(match)) {
                 rules[i] = rule;
-                /* Even at 20 Mpps the 32-bit hit_cnt cannot wrap
-                 * within one second optimization interval. */
                 subtable->hit_cnt++;
                 goto next;
             }
@@ -96,3 +224,16 @@  dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
 
     return found_map;
 }
+
+/* Generic lookup function that uses runtime provided mf bits for iterating. */
+uint32_t
+dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
+                              uint64_t *blocks_scratch,
+                              uint32_t keys_map,
+                              const struct netdev_flow_key *keys[],
+                              struct dpcls_rule **rules)
+{
+    return lookup_generic_impl(subtable, blocks_scratch, keys_map, keys, rules,
+                               subtable->mf_bits_set_unit0,
+                               subtable->mf_bits_set_unit1);
+}
diff --git a/lib/dpif-netdev-private.h b/lib/dpif-netdev-private.h
index 555856482..e1ceaa641 100644
--- a/lib/dpif-netdev-private.h
+++ b/lib/dpif-netdev-private.h
@@ -56,13 +56,15 @@  struct dpcls_rule {
  */
 typedef
 uint32_t (*dpcls_subtable_lookup_func)(struct dpcls_subtable *subtable,
+                                       uint64_t *blocks_scratch,
                                        uint32_t keys_map,
                                        const struct netdev_flow_key *keys[],
                                        struct dpcls_rule **rules);
 
-/* Prototype for generic lookup func, using same code path as before. */
+/* Prototype for generic lookup func, using generic scalar code path. */
 uint32_t
 dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
+                              uint64_t *blocks_scratch,
                               uint32_t keys_map,
                               const struct netdev_flow_key *keys[],
                               struct dpcls_rule **rules);
@@ -77,12 +79,22 @@  struct dpcls_subtable {
     uint32_t hit_cnt;            /* Number of match hits in subtable in current
                                     optimization interval. */
 
+    /* Miniflow fingerprint that the subtable matches on. The miniflow "bits"
+     * are used to select the actual dpcls lookup implementation at subtable
+     * creation time.
+     */
+    uint8_t mf_bits_set_unit0;
+    uint8_t mf_bits_set_unit1;
+
     /* The lookup function to use for this subtable. If there is a known
      * property of the subtable (eg: only 3 bits of miniflow metadata is
      * used for the lookup) then this can point at an optimized version of
      * the lookup function for this particular subtable. */
     dpcls_subtable_lookup_func lookup_func;
 
+    /* Caches the masks to match a packet to, reducing runtime calculations. */
+    uint64_t *mf_masks;
+
     struct netdev_flow_key mask; /* Wildcards for fields (const). */
     /* 'mask' must be the last field, additional space is allocated here. */
 };
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index b42ca35e3..1b92cd4c9 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -233,6 +233,15 @@  struct dpcls {
     odp_port_t in_port;
     struct cmap subtables_map;
     struct pvector subtables;
+
+    /* Region of memory for this DPCLS instance to use as scratch.
+     * Size is guaranteed to be large enough to hold all blocks required for
+     * the subtable's to match on. This allows each dpcls lookup to flatten
+     * the packet miniflows into this blocks_scratch area, without using
+     * variable length arrays. This region is allocated on subtable create, and
+     * will be resized as required if a larger subtable is added. */
+    uint64_t *blocks_scratch;
+    uint32_t blocks_scratch_size;
 };
 
 /* Data structure to keep packet order till fastpath processing. */
@@ -7649,6 +7658,7 @@  static void
 dpcls_subtable_destroy_cb(struct dpcls_subtable *subtable)
 {
     cmap_destroy(&subtable->rules);
+    ovsrcu_postpone(free, subtable->mf_masks);
     ovsrcu_postpone(free, subtable);
 }
 
@@ -7659,6 +7669,8 @@  dpcls_init(struct dpcls *cls)
 {
     cmap_init(&cls->subtables_map);
     pvector_init(&cls->subtables);
+    cls->blocks_scratch = NULL;
+    cls->blocks_scratch_size = 0;
 }
 
 static void
@@ -7686,6 +7698,7 @@  dpcls_destroy(struct dpcls *cls)
         }
         cmap_destroy(&cls->subtables_map);
         pvector_destroy(&cls->subtables);
+        ovsrcu_postpone(free, cls->blocks_scratch);
     }
 }
 
@@ -7701,7 +7714,28 @@  dpcls_create_subtable(struct dpcls *cls, const struct netdev_flow_key *mask)
     subtable->hit_cnt = 0;
     netdev_flow_key_clone(&subtable->mask, mask);
 
-    /* Decide which hash/lookup/verify function to use. */
+    /* The count of bits in the mask defines the space required for masks.
+     * Then call gen_masks() to create the appropriate masks, avoiding the cost
+     * of doing runtime calculations. */
+    uint32_t unit0 = count_1bits(mask->mf.map.bits[0]);
+    uint32_t unit1 = count_1bits(mask->mf.map.bits[1]);
+    subtable->mf_bits_set_unit0 = unit0;
+    subtable->mf_bits_set_unit1 = unit1;
+
+    subtable->mf_masks = xmalloc(sizeof(uint64_t) * (unit0 + unit1));
+    netdev_flow_key_gen_masks(mask, subtable->mf_masks, unit0, unit1);
+
+    /* Allocate blocks scratch space only if subtable requires more size than
+     * is currently allocated. */
+    const uint32_t blocks_required_per_pkt = unit0 + unit1;
+    if (cls->blocks_scratch_size < blocks_required_per_pkt) {
+        free(cls->blocks_scratch);
+        cls->blocks_scratch = xmalloc(sizeof(uint64_t) * NETDEV_MAX_BURST *
+                                      blocks_required_per_pkt);
+        cls->blocks_scratch_size = blocks_required_per_pkt;
+    }
+
+    /* Assign the generic lookup - this works with any miniflow fingerprint. */
     subtable->lookup_func = dpcls_subtable_lookup_generic;
 
     cmap_insert(&cls->subtables_map, &subtable->cmap_node, mask->hash);
@@ -7846,6 +7880,43 @@  dpcls_remove(struct dpcls *cls, struct dpcls_rule *rule)
     }
 }
 
+/* Inner loop for mask generation of a unit, see netdev_flow_key_gen_masks. */
+static inline void
+netdev_flow_key_gen_mask_unit(uint64_t iter,
+                              const uint64_t count,
+                              uint64_t *mf_masks)
+{
+    int i;
+    for (i = 0; i < count; i++) {
+        uint64_t lowest_bit = (iter & -iter);
+        iter &= ~lowest_bit;
+        mf_masks[i] = (lowest_bit - 1);
+    }
+    /* Checks that count has covered all bits in the iter bitmap. */
+    ovs_assert(iter == 0);
+}
+
+/* Generate a mask for each block in the miniflow, based on the bits set. This
+ * allows easily masking packets with the generated array here, without
+ * calculations. This replaces runtime-calculating the masks.
+ * @param key The table to generate the mf_masks for
+ * @param mf_masks Pointer to a u64 array of at least *mf_bits* in size
+ * @param mf_bits_total Number of bits set in the whole miniflow (both units)
+ * @param mf_bits_unit0 Number of bits set in unit0 of the miniflow
+ */
+void
+netdev_flow_key_gen_masks(const struct netdev_flow_key *tbl,
+                          uint64_t *mf_masks,
+                          const uint32_t mf_bits_u0,
+                          const uint32_t mf_bits_u1)
+{
+    uint64_t iter_u0 = tbl->mf.map.bits[0];
+    uint64_t iter_u1 = tbl->mf.map.bits[1];
+
+    netdev_flow_key_gen_mask_unit(iter_u0, mf_bits_u0, &mf_masks[0]);
+    netdev_flow_key_gen_mask_unit(iter_u1, mf_bits_u1, &mf_masks[mf_bits_u0]);
+}
+
 /* Returns true if 'target' satisfies 'key' in 'mask', that is, if each 1-bit
  * in 'mask' the values in 'key' and 'target' are the same. */
 bool
@@ -7886,6 +7957,7 @@  dpcls_lookup(struct dpcls *cls, const struct netdev_flow_key *keys[],
     BUILD_ASSERT_DECL(MAP_BITS >= NETDEV_MAX_BURST);
 
     struct dpcls_subtable *subtable;
+    uint64_t *blocks_scratch = cls->blocks_scratch;
 
     uint32_t keys_map = TYPE_MAXIMUM(uint32_t); /* Set all bits. */
 
@@ -7906,7 +7978,8 @@  dpcls_lookup(struct dpcls *cls, const struct netdev_flow_key *keys[],
      * non-overlapping. */
     PVECTOR_FOR_EACH (subtable, &cls->subtables) {
         /* Call the subtable specific lookup function. */
-        found_map = subtable->lookup_func(subtable, keys_map, keys, rules);
+        found_map = subtable->lookup_func(subtable, blocks_scratch, keys_map,
+                                          keys, rules);
 
         /* Count the number of subtables searched for this packet match. This
          * estimates the "spread" of subtables looked at per matched packet. */