[ovs-dev] [PATCH v2 01/12] dpcls: Use 32 packet batches for lookups.

Fischetti, Antonio antonio.fischetti at intel.com
Fri Oct 14 10:25:24 UTC 2016


Thanks for your comments Daniele, my replies inline.

Antonio

> -----Original Message-----
> From: dev [mailto:dev-bounces at openvswitch.org] On Behalf Of Daniele Di
> Proietto
> Sent: Friday, October 14, 2016 3:08 AM
> To: Bodireddy, Bhanuprakash <bhanuprakash.bodireddy at intel.com>
> Cc: dev at openvswitch.org
> Subject: Re: [ovs-dev] [PATCH v2 01/12] dpcls: Use 32 packet batches for
> lookups.
> 
> I think this looks good, thanks.
> 
> I have a few comments inline to simplify the code a little bit more.
> 
> 2016-10-13 2:58 GMT-07:00 Bhanuprakash Bodireddy <
> bhanuprakash.bodireddy at intel.com>:
> 
> > This patch increases the number of packets processed in a batch during a
> > lookup from 16 to 32. Processing batches of 32 packets improves
> > performance and also one of the internal loops can be avoided here.
> >
> > Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
> > Co-authored-by: Bhanuprakash Bodireddy
> <bhanuprakash.bodireddy at intel.com>
> > ---
> >  lib/dpif-netdev.c | 110 +++++++++++++++++++++++-------
> > ------------------------
> >  1 file changed, 47 insertions(+), 63 deletions(-)
> >
> > diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> > index eb9f764..3b3556a 100644
> > --- a/lib/dpif-netdev.c
> > +++ b/lib/dpif-netdev.c
> > @@ -4985,23 +4985,21 @@ dpcls_lookup(struct dpcls *cls, const struct
> > netdev_flow_key keys[],
> >               int *num_lookups_p)
> >  {
> >      /* The received 'cnt' miniflows are the search-keys that will be
> > processed
> > -     * in batches of 16 elements.  N_MAPS will contain the number of
> these
> > -     * 16-elements batches.  i.e. for 'cnt' = 32, N_MAPS will be 2.
> The
> > batch
> > -     * size 16 was experimentally found faster than 8 or 32. */
> > -    typedef uint16_t map_type;
> > +     * to find a matching entry into the available subtables.
> > +     * The number of bits in map_type is equal to NETDEV_MAX_BURST. */
> > +    typedef uint32_t map_type;
> >  #define MAP_BITS (sizeof(map_type) * CHAR_BIT)
> > +    BUILD_ASSERT_DECL(MAP_BITS >= NETDEV_MAX_BURST);
> >
> > -#if !defined(__CHECKER__) && !defined(_WIN32)
> > -    const int N_MAPS = DIV_ROUND_UP(cnt, MAP_BITS);
> > -#else
> > -    enum { N_MAPS = DIV_ROUND_UP(NETDEV_MAX_BURST, MAP_BITS) };
> > -#endif
> > -    map_type maps[N_MAPS];
> >      struct dpcls_subtable *subtable;
> >
> > -    memset(maps, 0xff, sizeof maps);
> > -    if (cnt % MAP_BITS) {
> > -        maps[N_MAPS - 1] >>= MAP_BITS - cnt % MAP_BITS; /* Clear extra
> > bits. */
> > +    map_type keys_map = 0xffffffff;
> >
> 
> Can we use TYPE_MAXIMUM(map_type) instead of 0xffffffff?
[Antonio F] Sure, will do.

> 
> 
> > +    map_type found_map;
> > +    uint32_t hashes[MAP_BITS];
> > +    const struct cmap_node *nodes[MAP_BITS];
> >
> 
> The above three variables can be moved inside the look
[Antonio F] We moved them outside of the loop, otherwise we found
a slight performance drop.

> 
> 
> > +
> > +    if (OVS_UNLIKELY(cnt != NETDEV_MAX_BURST)) {
> >
> 
> I'm not sure the OVS_UNLIKELY is important here.
> 
> I'll leave it up to you.
[Antonio F] Agree, it's better to remove it.  It could make
sense in a test environment, with EMC disabled.

> 
> 
> > +        keys_map >>= NETDEV_MAX_BURST - cnt; /* Clear extra bits. */
> >      }
> >      memset(rules, 0, cnt * sizeof *rules);
> >
> > @@ -5017,59 +5015,45 @@ dpcls_lookup(struct dpcls *cls, const struct
> > netdev_flow_key keys[],
> >      PVECTOR_FOR_EACH (subtable, &cls->subtables) {
> >          const struct netdev_flow_key *mkeys = keys;
> >          struct dpcls_rule **mrules = rules;
> >
> 
> Are the two variables above still necessary?  I think they're not
[Antonio F] You're right, will remove.

> 
> 
> > -        map_type remains = 0;
> > -        int m;
> > -
> > -        BUILD_ASSERT_DECL(sizeof remains == sizeof *maps);
> > -
> > -        /* Loops on each batch of 16 search-keys. */
> > -        for (m = 0; m < N_MAPS; m++, mkeys += MAP_BITS, mrules +=
> > MAP_BITS) {
> > -            uint32_t hashes[MAP_BITS];
> > -            const struct cmap_node *nodes[MAP_BITS];
> > -            unsigned long map = maps[m];
> > -            int i;
> > -
> > -            if (!map) {
> > -                continue; /* Skip empty maps. */
> > -            }
> > -
> > -            /* Compute hashes for the remaining keys.  Each search-key
> is
> > -             * masked with the subtable's mask to avoid hashing the
> > wildcarded
> > -             * bits. */
> > -            ULLONG_FOR_EACH_1(i, map) {
> > -                hashes[i] = netdev_flow_key_hash_in_mask(&mkeys[i],
> > -                                                         &subtable-
> >mask);
> > -            }
> > -            /* Lookup. */
> > -            map = cmap_find_batch(&subtable->rules, map, hashes,
> nodes);
> > -            /* Check results.  When the i-th bit of 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. */
> > -            ULLONG_FOR_EACH_1(i, map) {
> > -                struct dpcls_rule *rule;
> > -
> > -                CMAP_NODE_FOR_EACH (rule, cmap_node, nodes[i]) {
> > -                    if (OVS_LIKELY(dpcls_rule_matches_key(rule,
> > &mkeys[i]))) {
> > -                        mrules[i] = rule;
> > -                        /* Even at 20 Mpps the 32-bit hit_cnt cannot
> wrap
> > -                         * within one second optimization interval  */
> > -                        subtable->hit_cnt++;
> > -                        lookups_match += subtable_pos;
> > -                        goto next;
> > -                    }
> > +        int i;
> >
> 
> 
> 
> > +        found_map = keys_map;
> >
> 
> I believe the above to be not necessary.  We can pass keys_map directly to
> cmap_find_batch()
[Antonio F] Right, will do.

> 
> 
> > +
> > +        /* Compute hashes for the remaining keys.  Each search-key is
> > +         * masked with the subtable's mask to avoid hashing the
> wildcarded
> > +         * bits. */
> > +        ULLONG_FOR_EACH_1(i, keys_map) {
> > +            hashes[i] = netdev_flow_key_hash_in_mask(&mkeys[i],
> > +                                                     &subtable->mask);
> > +        }
> > +        /* Lookup. */
> > +        found_map = cmap_find_batch(&subtable->rules, found_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. */
> > +        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,
> &mkeys[i])))
> > {
> > +                    mrules[i] = rule;
> > +                    /* Even at 20 Mpps the 32-bit hit_cnt cannot wrap
> > +                     * within one second optimization interval. */
> > +                    subtable->hit_cnt++;
> > +                    lookups_match += subtable_pos;
> > +                    goto next;
> >                  }
> > -                /* None of the found rules was a match. Reset the i-th
> > bit to
> > -                 * keep searching in the next subtable. */
> > -                ULLONG_SET0(map, i);  /* Did not match. */
> > -            next:
> > -                ;                     /* Keep Sparse happy. */
> >              }
> > -            maps[m] &= ~map;          /* Clear the found rules. */
> > -            remains |= maps[m];
> > +            /* 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. */
> > +        next:
> > +            ;                     /* Keep Sparse happy. */
> >          }
> > -        if (!remains) {
> > +        keys_map &= ~found_map;             /* Clear the found rules.
> */
> > +        if (!keys_map) {
> >              if (num_lookups_p) {
> >                  *num_lookups_p = lookups_match;
> >              }
> > --
> > 2.4.11
> >
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> >
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