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Date: Mon, 30 Mar 2020 08:34:48 +0800
From: Tonghao Zhang <xiangxia.m.yue@...il.com>
To: Pravin Shelar <pshelar@....org>
Cc: Linux Kernel Network Developers <netdev@...r.kernel.org>,
ovs dev <dev@...nvswitch.org>, Andy Zhou <azhou@....org>
Subject: Re: [PATCH net-next v1 1/3] net: openvswitch: expand the meters
number supported
On Mon, Mar 30, 2020 at 12:46 AM Pravin Shelar <pshelar@....org> wrote:
>
> On Sat, Mar 28, 2020 at 8:46 AM <xiangxia.m.yue@...il.com> wrote:
> >
> > From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> >
> > 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 <pshelar@....org>
> > Cc: Andy Zhou <azhou@....org>
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> > ---
> > 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.
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.
>
> > 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
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