> -----Original Message-----
> From: Ilya Maximets [mailto:[email protected]]
> Sent: Wednesday, July 17, 2019 11:14 AM
> To: Van Haaren, Harry <[email protected]>; [email protected]
> Cc: [email protected]; [email protected]; Stokes, Ian
> <[email protected]>
> Subject: Re: [PATCH v11 4/5] dpif-netdev: Refactor generic implementation
<snip>
> >> diff --git a/lib/dpif-netdev-lookup-generic.c b/lib/dpif-netdev-lookup-
> generic.c
> >> index 833abf54f..abd166fc3 100644
> >> --- a/lib/dpif-netdev-lookup-generic.c
> >> +++ b/lib/dpif-netdev-lookup-generic.c
> >> @@ -30,68 +30,210 @@
> >> #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);
> >
> > dpif_netdev_lookup_generic?
> >
> > BTW, this might be not needed if we'll remove logging in the patch #5.
Refer to feedback on 5/5 just now - leaving the logging in the implementation
is the better solution IMO.
> >> +/* 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 */
> >
> > Missed comment (style).
Will fix in v12.
<snip>
> >> + /* 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);
>
> You mentioned before that 'hash_words64_inline()' has a different finish
> value, but I don't think that it matters to preserve the actual value of
> a hash here. Even 'hash_words64()' should be fine, because it checks if
> the argument is a compile time constant and calls the 'hash_words64_inline'
> in this case.
Be very careful reading the hash.h inline functions, there's lots of them, and
they're #ifdef-ed based on platform etc. It is quite confusing IMO.
Notice the call I'm making is to "hash_add_words64()", and not "hash_words64()".
The hash_add_words64() only provides just the loop, and does not call
hash_finish(),
and hash_finish() is called by my code above with the correct hash_finish()
value.
You're right that hash_words64() calls the _inline() flavor if the n_words
variable is constant, and would end up calling the hash_finish() version, and
hence is not valid.
I've prototyped a variety of different code-paths here, the above (as v11)
makes the most re-use of the existing hash code. The v10 and before is the
same code, but with own loops rolled.
I suggest to use the v11 version as it re-uses the hash loops - which is
cleaner.
> >> - /* 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;
> >> }
> >> }
> >> - /* None of the found rules was a match. Reset the i-th bit to
> >> - * keep searching this key in the next subtable. */
> >> - ULLONG_SET0(found_map, i); /* Did not match. */
> >> +
> >> + /* None of the found rules was a match. Clear the i-th bit to
> >> + * search for this key in the next subtable. */
> >> + ULLONG_SET0(found_map, i);
> >> next:
> >> - ; /* Keep Sparse happy. */
> >> + ; /* Keep Sparse happy. */
> >
> > You're changing the indentation of this comment back and forth few times
> > around the patch series.
Will investigate and fix in v12.
<snip>
> >> -/* 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);
> >> @@ -84,13 +86,13 @@ struct dpcls_subtable {
> >> 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
> >> + /* 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 */
> >> + /* Caches the masks to match a packet to, reducing runtime
> calculations. */
> >
> > Above two changes should be part of the previous patches.
> >
> > BTW, introduction of the 'mf_masks' and 'mf_bits*' should happen in this
> patch,
> > not in the "dpif-netdev: Move dpcls lookup structures to .h".
Will investigate and fix in v12.
> >> uint64_t *mf_masks;
> >>
> >> struct netdev_flow_key mask; /* Wildcards for fields (const). */
> >> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> >> index b42ca35e3..8acc1445a 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 garaunteed to be large enough to hold all blocks required
> for
> >
> > s/garaunteed/guaranteed/
Typo - will fix.
> >> + * the subtable's to match on. This allows each dpcls lookup to
> flatten
> >> + * the packet miniflows into this blocks_scratch area, without using
> >> + * variable lenght arrays. This region is allocated on subtable
> create, and
> >
> > s/lenght/length/
Typo - will fix.
<snip>
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