Subject: Re: [ovs-dev] [PATCH net-next v1 1/3] net: openvswitch: expand the meters number supported

From: William Tu <[email-masked]>
Date: Wed, 8 Apr 2020 08:09:16 -0700

On Wed, Apr 01, 2020 at 06:50:09PM +0800, Tonghao Zhang wrote:
> On Tue, Mar 31, 2020 at 11:57 AM Pravin Shelar <[email-masked]> wrote:
> >
> > On Sun, Mar 29, 2020 at 5:35 PM Tonghao Zhang <[email-masked]> wrote:
> > >
> > > On Mon, Mar 30, 2020 at 12:46 AM Pravin Shelar <[email-masked]> wrote:
> > > >
> > > > On Sat, Mar 28, 2020 at 8:46 AM <[email-masked]> wrote:
> > > > >
> > > > > From: Tonghao Zhang <[email-masked]>
> > > > >
> > > > > In kernel datapath of Open vSwitch, there are only 1024
> > > > > buckets of meter in one dp. If installing more than 1024
> > > > > (e.g. 8192) meters, it may lead to the performance drop.
> > > > > But in some case, for example, Open vSwitch used as edge
> > > > > gateway, there should be 200,000+ at least, meters used for
> > > > > IP address bandwidth limitation.
> > > > >
> > > > > [Open vSwitch userspace datapath has this issue too.]
> > > > >
> > > > > For more scalable meter, this patch expands the buckets
> > > > > when necessary, so we can install more meters in the datapath.
> > > > >
> > > > > * Introducing the struct *dp_meter_instance*, it's easy to
> > > > >   expand meter though change the *ti* point in the struct
> > > > >   *dp_meter_table*.
> > > > > * Using kvmalloc_array instead of kmalloc_array.
> > > > >
> > > > Thanks for working on this, I have couple of comments.
> > > >
> > > > > Cc: Pravin B Shelar <[email-masked]>
> > > > > Cc: Andy Zhou <[email-masked]>
> > > > > Signed-off-by: Tonghao Zhang <[email-masked]>
> > > > > ---
> > > > >  net/openvswitch/datapath.h |   2 +-
> > > > >  net/openvswitch/meter.c    | 168 ++++++++++++++++++++++++++++++-------
> > > > >  net/openvswitch/meter.h    |  17 +++-
> > > > >  3 files changed, 153 insertions(+), 34 deletions(-)
> > > > >
> > > > > diff --git a/net/openvswitch/datapath.h b/net/openvswitch/datapath.h
> > > > > index e239a46c2f94..785105578448 100644
> > > > > --- a/net/openvswitch/datapath.h
> > > > > +++ b/net/openvswitch/datapath.h
> > > > > @@ -82,7 +82,7 @@ struct datapath {
> > > > >         u32 max_headroom;
> > > > >
> > > > >         /* Switch meters. */
> > > > > -       struct hlist_head *meters;
> > > > > +       struct dp_meter_table *meters;
> > > > >  };
> > > > >
> > > > >  /**
> > > > > diff --git a/net/openvswitch/meter.c b/net/openvswitch/meter.c
> > > > > index 5010d1ddd4bd..98003b201b45 100644
> > > > > --- a/net/openvswitch/meter.c
> > > > > +++ b/net/openvswitch/meter.c
> > > > > @@ -47,40 +47,136 @@ static void ovs_meter_free(struct dp_meter *meter)
> > > > >         kfree_rcu(meter, rcu);
> > > > >  }
> > > > >
> > > > > -static struct hlist_head *meter_hash_bucket(const struct datapath *dp,
> > > > > +static struct hlist_head *meter_hash_bucket(struct dp_meter_instance *ti,
> > > > >                                             u32 meter_id)
> > > > >  {
> > > > > -       return &dp->meters[meter_id & (METER_HASH_BUCKETS - 1)];
> > > > > +       u32 hash = jhash_1word(meter_id, ti->hash_seed);
> > > > > +
> > > > I do not see any need to hash meter-id, can you explain it.
> > > >
> > > > > +       return &ti->buckets[hash & (ti->n_buckets - 1)];
> > > > >  }
> > > > >
> > > > >  /* Call with ovs_mutex or RCU read lock. */
> > > > > -static struct dp_meter *lookup_meter(const struct datapath *dp,
> > > > > +static struct dp_meter *lookup_meter(const struct dp_meter_table *tbl,
> > > > >                                      u32 meter_id)
> > > > >  {
> > > > > +       struct dp_meter_instance *ti = rcu_dereference_ovsl(tbl->ti);
> > > > >         struct dp_meter *meter;
> > > > >         struct hlist_head *head;
> > > > >
> > > > > -       head = meter_hash_bucket(dp, meter_id);
> > > > > -       hlist_for_each_entry_rcu(meter, head, dp_hash_node,
> > > > > -                               lockdep_ovsl_is_held()) {
> > > > > +       head = meter_hash_bucket(ti, meter_id);
> > > > > +       hlist_for_each_entry_rcu(meter, head, hash_node[ti->node_ver],
> > > > > +                                lockdep_ovsl_is_held()) {
> > > > >                 if (meter->id == meter_id)
> > > > >                         return meter;
> > > > >         }
> > > > > +
> > > > This patch is expanding meter table linearly with number meters added
> > > > to datapath. so I do not see need to have hash table. it can be a
> > > > simple array. This would also improve lookup efficiency.
> > > > For hash collision we could find next free slot in array. let me know
> > > > what do you think about this approach.
> > > Hi Pravin
> > > If we use the simple array, when inserting the meter, for hash collision, we can
> > > find next free slot, but one case, when there are many meters in the array.
> > > we may find many slot for the free slot.
> > > And when we lookup the meter, for hash collision, we may find many
> > > array slots, and
> > > then find it, or that meter does not exist in the array, In that case,
> > > there may be a lookup performance
> > > drop.
> > >
> > I was thinking that users can insure that there are no hash collision,
> > but time complexity of negative case is expensive. so I am fine with
> > the hash table.

IIUC, there will be hash collision. meter id is an 32-bit value.
Currenly in lib/dpif-netdev.c, MAX_METERS = 65536.

I think what Pravin suggest is to use another hash function to make
the hash table more condense. Ex: hash1 and hash2. 
For lookup, if hash1(key) misses, then try hash2(key).

William

> Hi Pravi
> I check again the meter implementation of ovs, ovs-vswitchd use the id-pool to
> get a valid meter-id which passed to kernel, so there is no hash collision. You
> are right. we use the single array is the better solution.
> > > For hash meter-id in meter_hash_bucket, I am not 100% sure it is
> > > useful. it just update
> > > hash_seed when expand meters. For performance, we can remove it. Thanks.
> > ok.
> >
> > > > >         return NULL;
> > > > >  }
> > > > >
> > > > > -static void attach_meter(struct datapath *dp, struct dp_meter *meter)
> > > > > +static struct dp_meter_instance *dp_meter_instance_alloc(const int size)
> > > > > +{
> > > > > +       struct dp_meter_instance *ti;
> > > > > +       int i;
> > > > > +
> > > > > +       ti = kmalloc(sizeof(*ti), GFP_KERNEL);
> > > > > +       if (!ti)
> > > > > +               return NULL;
> > > > > +
> > > > > +       ti->buckets = kvmalloc_array(size, sizeof(struct hlist_head),
> > > > > +                                    GFP_KERNEL);
> > > > > +       if (!ti->buckets) {
> > > > > +               kfree(ti);
> > > > > +               return NULL;
> > > > > +       }
> > > > > +
> > > > > +       for (i = 0; i < size; i++)
> > > > > +               INIT_HLIST_HEAD(&ti->buckets[i]);
> > > > > +
> > > > > +       ti->n_buckets = size;
> > > > > +       ti->node_ver = 0;
> > > > > +       get_random_bytes(&ti->hash_seed, sizeof(u32));
> > > > > +
> > > > > +       return ti;
> > > > > +}
> > > > > +
> > > > > +static void dp_meter_instance_free_rcu(struct rcu_head *rcu)
> > > > >  {
> > > > > -       struct hlist_head *head = meter_hash_bucket(dp, meter->id);
> > > > > +       struct dp_meter_instance *ti;
> > > > >
> > > > > -       hlist_add_head_rcu(&meter->dp_hash_node, head);
> > > > > +       ti = container_of(rcu, struct dp_meter_instance, rcu);
> > > > > +       kvfree(ti->buckets);
> > > > > +       kfree(ti);
> > > > >  }
> > > > >
> > > > > -static void detach_meter(struct dp_meter *meter)
> > > > > +static void dp_meter_instance_insert(struct dp_meter_instance *ti,
> > > > > +                                    struct dp_meter *meter)
> > > > > +{
> > > > > +       struct hlist_head *head = meter_hash_bucket(ti, meter->id);
> > > > > +
> > > > > +       hlist_add_head_rcu(&meter->hash_node[ti->node_ver], head);
> > > > > +}
> > > > > +
> > > > > +static void dp_meter_instance_remove(struct dp_meter_instance *ti,
> > > > > +                                    struct dp_meter *meter)
> > > > >  {
> > > > > +       hlist_del_rcu(&meter->hash_node[ti->node_ver]);
> > > > > +}
> > > > > +
> > > > > +static struct dp_meter_instance *
> > > > > +dp_meter_instance_expand(struct dp_meter_instance *ti)
> > > > > +{
> > > > > +       struct dp_meter_instance *new_ti;
> > > > > +       int i;
> > > > > +
> > > > > +       new_ti = dp_meter_instance_alloc(ti->n_buckets * 2);
> > > > > +       if (!new_ti)
> > > > > +               return NULL;
> > > > > +
> > > > > +       new_ti->node_ver = !ti->node_ver;
> > > > > +
> > > > > +       for (i = 0; i < ti->n_buckets; i++) {
> > > > > +               struct hlist_head *head = &ti->buckets[i];
> > > > > +               struct dp_meter *meter;
> > > > > +
> > > > > +               hlist_for_each_entry_rcu(meter, head, hash_node[ti->node_ver],
> > > > > +                                        lockdep_ovsl_is_held())
> > > > > +                       dp_meter_instance_insert(new_ti, meter);
> > > > > +       }
> > > > > +
> > > > > +       return new_ti;
> > > > > +}
> > > > > +
> > > > > +static void attach_meter(struct dp_meter_table *tbl, struct dp_meter *meter)
> > > > > +{
> > > > > +       struct dp_meter_instance *new_ti;
> > > > > +       struct dp_meter_instance *ti;
> > > > > +
> > > > > +       ti = rcu_dereference_ovsl(tbl->ti);
> > > > > +       dp_meter_instance_insert(ti, meter);
> > > > > +
> > > > > +       /* operate the counter safely, because called with ovs_lock. */
> > > > > +       tbl->count++;
> > > > > +
> > > > > +       if (tbl->count > ti->n_buckets) {
> > > > > +               new_ti = dp_meter_instance_expand(ti);
> > > > > +
> > > >
> > > >
> > > > > +               if (new_ti) {
> > > > > +                       rcu_assign_pointer(tbl->ti, new_ti);
> > > > > +                       call_rcu(&ti->rcu, dp_meter_instance_free_rcu);
> > > > > +               }
> > > > > +       }
> > > > > +}
> > > > > +
> > > > > +static void detach_meter(struct dp_meter_table *tbl, struct dp_meter *meter)
> > > > > +{
> > > > > +       struct dp_meter_instance *ti = rcu_dereference_ovsl(tbl->ti);
> > > > > +
> > > > >         ASSERT_OVSL();
> > > > > -       if (meter)
> > > > > -               hlist_del_rcu(&meter->dp_hash_node);
> > > > > +       if (meter) {
> > > > > +               /* operate the counter safely, because called with ovs_lock. */
> > > > > +               tbl->count--;
> > > > > +               dp_meter_instance_remove(ti, meter);
> > > > > +       }
> > > > >  }
> > > > >
> > > > >  static struct sk_buff *
> > > > > @@ -303,9 +399,9 @@ static int ovs_meter_cmd_set(struct sk_buff *skb, struct genl_info *info)
> > > > >         meter_id = nla_get_u32(a[OVS_METER_ATTR_ID]);
> > > > >
> > > > >         /* Cannot fail after this. */
> > > > > -       old_meter = lookup_meter(dp, meter_id);
> > > > > -       detach_meter(old_meter);
> > > > > -       attach_meter(dp, meter);
> > > > > +       old_meter = lookup_meter(dp->meters, meter_id);
> > > > > +       detach_meter(dp->meters, old_meter);
> > > > > +       attach_meter(dp->meters, meter);
> > > > >         ovs_unlock();
> > > > >
> > > > >         /* Build response with the meter_id and stats from
> > > > > @@ -365,7 +461,7 @@ static int ovs_meter_cmd_get(struct sk_buff *skb, struct genl_info *info)
> > > > >         }
> > > > >
> > > > >         /* Locate meter, copy stats. */
> > > > > -       meter = lookup_meter(dp, meter_id);
> > > > > +       meter = lookup_meter(dp->meters, meter_id);
> > > > >         if (!meter) {
> > > > >                 err = -ENOENT;
> > > > >                 goto exit_unlock;
> > > > > @@ -416,13 +512,13 @@ static int ovs_meter_cmd_del(struct sk_buff *skb, struct genl_info *info)
> > > > >                 goto exit_unlock;
> > > > >         }
> > > > >
> > > > > -       old_meter = lookup_meter(dp, meter_id);
> > > > > +       old_meter = lookup_meter(dp->meters, meter_id);
> > > > >         if (old_meter) {
> > > > >                 spin_lock_bh(&old_meter->lock);
> > > > >                 err = ovs_meter_cmd_reply_stats(reply, meter_id, old_meter);
> > > > >                 WARN_ON(err);
> > > > >                 spin_unlock_bh(&old_meter->lock);
> > > > > -               detach_meter(old_meter);
> > > > > +               detach_meter(dp->meters, old_meter);
> > > > >         }
> > > > >         ovs_unlock();
> > > > >         ovs_meter_free(old_meter);
> > > > > @@ -452,7 +548,7 @@ bool ovs_meter_execute(struct datapath *dp, struct sk_buff *skb,
> > > > >         int i, band_exceeded_max = -1;
> > > > >         u32 band_exceeded_rate = 0;
> > > > >
> > > > > -       meter = lookup_meter(dp, meter_id);
> > > > > +       meter = lookup_meter(dp->meters, meter_id);
> > > > >         /* Do not drop the packet when there is no meter. */
> > > > >         if (!meter)
> > > > >                 return false;
> > > > > @@ -570,32 +666,44 @@ struct genl_family dp_meter_genl_family __ro_after_init = {
> > > > >
> > > > >  int ovs_meters_init(struct datapath *dp)
> > > > >  {
> > > > > -       int i;
> > > > > +       struct dp_meter_instance *ti;
> > > > > +       struct dp_meter_table *tbl;
> > > > >
> > > > > -       dp->meters = kmalloc_array(METER_HASH_BUCKETS,
> > > > > -                                  sizeof(struct hlist_head), GFP_KERNEL);
> > > > > +       tbl = kmalloc(sizeof(*tbl), GFP_KERNEL);
> > > > > +       if (!tbl)
> > > > > +               return -ENOMEM;
> > > > >
> > > > > -       if (!dp->meters)
> > > > > +       tbl->count = 0;
> > > > > +
> > > > > +       ti = dp_meter_instance_alloc(METER_HASH_BUCKETS);
> > > > > +       if (!ti) {
> > > > > +               kfree(tbl);
> > > > >                 return -ENOMEM;
> > > > > +       }
> > > > >
> > > > > -       for (i = 0; i < METER_HASH_BUCKETS; i++)
> > > > > -               INIT_HLIST_HEAD(&dp->meters[i]);
> > > > > +       rcu_assign_pointer(tbl->ti, ti);
> > > > > +       dp->meters = tbl;
> > > > >
> > > > >         return 0;
> > > > >  }
> > > > >
> > > > >  void ovs_meters_exit(struct datapath *dp)
> > > > >  {
> > > > > +       struct dp_meter_table *tbl = dp->meters;
> > > > > +       struct dp_meter_instance *ti = rcu_dereference_ovsl(tbl->ti);
> > > > >         int i;
> > > > >
> > > > > -       for (i = 0; i < METER_HASH_BUCKETS; i++) {
> > > > > -               struct hlist_head *head = &dp->meters[i];
> > > > > +       for (i = 0; i < ti->n_buckets; i++) {
> > > > > +               struct hlist_head *head = &ti->buckets[i];
> > > > >                 struct dp_meter *meter;
> > > > >                 struct hlist_node *n;
> > > > >
> > > > > -               hlist_for_each_entry_safe(meter, n, head, dp_hash_node)
> > > > > -                       kfree(meter);
> > > > > +               hlist_for_each_entry_safe(meter, n, head,
> > > > > +                                         hash_node[ti->node_ver])
> > > > > +                       ovs_meter_free(meter);
> > > > >         }
> > > > >
> > > > > -       kfree(dp->meters);
> > > > > +       kvfree(ti->buckets);
> > > > > +       kfree(ti);
> > > > > +       kfree(tbl);
> > > > >  }
> > > > > diff --git a/net/openvswitch/meter.h b/net/openvswitch/meter.h
> > > > > index f645913870bd..bc84796d7d4d 100644
> > > > > --- a/net/openvswitch/meter.h
> > > > > +++ b/net/openvswitch/meter.h
> > > > > @@ -30,9 +30,7 @@ struct dp_meter_band {
> > > > >  struct dp_meter {
> > > > >         spinlock_t lock;    /* Per meter lock */
> > > > >         struct rcu_head rcu;
> > > > > -       struct hlist_node dp_hash_node; /*Element in datapath->meters
> > > > > -                                        * hash table.
> > > > > -                                        */
> > > > > +       struct hlist_node hash_node[2];
> > > > >         u32 id;
> > > > >         u16 kbps:1, keep_stats:1;
> > > > >         u16 n_bands;
> > > > > @@ -42,6 +40,19 @@ struct dp_meter {
> > > > >         struct dp_meter_band bands[];
> > > > >  };
> > > > >
> > > > > +struct dp_meter_instance {
> > > > > +       struct hlist_head *buckets;
> > > > > +       struct rcu_head rcu;
> > > > > +       u32 n_buckets;
> > > > > +       u32 hash_seed;
> > > > > +       u8 node_ver;
> > > > > +};
> > > > > +
> > > > > +struct dp_meter_table {
> > > > > +       struct dp_meter_instance __rcu *ti;
> > > > > +       u32 count;
> > > > > +};
> > > > > +
> > > > >  extern struct genl_family dp_meter_genl_family;
> > > > >  int ovs_meters_init(struct datapath *dp);
> > > > >  void ovs_meters_exit(struct datapath *dp);
> > > > > --
> > > > > 2.23.0
> > > > >
> > >
> > >
> > >
> > > --
> > > Best regards, Tonghao
> 
> 
> 
> -- 
> Best regards, Tonghao
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