> On Feb 19, 2024, at 3:28 PM, Abdullah Ömer Yamaç <aomerya...@gmail.com> wrote:
>
> Hello,
>
> Let me explain a use case;
>
> I have a hash table whose key value is IP addresses, and data (let's say the
> username of the IP) is related to the IP address. The key point is matching
> these data with flows. Flows are dynamic, and this hash table is dynamic, as
> well; both can change anytime. For example, when a flow starts, we look up
> the hash table with the corresponding IP and retrieve the username. We need
> to hold this username until the flow terminates, although we removed this IP
> key from the hash table (multithread). That's why we have RCU and defer queue
> is necessary for high performance. In my application, I need to know the
> number of IP-username entries. These numbers can be calculated by
> rte_hash_count - defer queue size.
The entries in the defer queue are not reclaimed (there is a probability that
all of them can be reclaimed) and hence they are not available for allocation.
So, rte_hash_count - defer queue size might not give you the correct number you
are expecting.
Currently, there is no API in hash library that forces a reclaim. Does it makes
sense to have an API that just does the reclaim (and returns the number of
entries pending in the defer queue)? A call to rte_hash_count should provide
the exact count you are looking for.
>
> I think if you need a non-blocking and multithreaded hash table, an
> RCU-enabled hash table is necessary. Also, this API is necessary if you need
> to get the actual matchable size.
>
>
>
>
>
> On Mon, Feb 19, 2024 at 8:36 PM Medvedkin, Vladimir
> <vladimir.medved...@intel.com> wrote:
> Hi Abdullah,
>
> Could you please tell more about use cases where this API may be useful?
>
> >a new API to get the hidden key count in the hash table if the rcu qsbr is
> >enabled
>
> Here in commit message and down below in doxygen comments, I think this
> statement should be more specific because rcu can be created with
> RTE_HASH_QSBR_MODE_SYNC mode i.e. without defer queue.
>
> Also, new API must be reflected in release notes
>
> On 07/02/2024 15:33, Abdullah Ömer Yamaç wrote:
> > This patch introduce a new API to get the hidden key count in the hash
> > table if the rcu qsbr is enabled. When using rte_hash_count with rcu
> > qsbr enabled, it will return the number of elements that are not in the
> > free queue. Unless rte_rcu_qsbr_dq_reclaim is called, the number of
> > elements in the defer queue will not be counted and freed. Therefore I
> > added a new API to get the number of hidden (defer queue) elements
> > in the hash table. Then the user can calculate the total number of
> > elements that are available in the hash table.
> >
> > Signed-off-by: Abdullah Ömer Yamaç <aomerya...@gmail.com>
> >
> > ---
> > Cc: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> > Cc: Yipeng Wang <yipeng1.w...@intel.com>
> > Cc: Sameh Gobriel <sameh.gobr...@intel.com>
> > Cc: Bruce Richardson <bruce.richard...@intel.com>
> > Cc: Vladimir Medvedkin <vladimir.medved...@intel.com>
> > ---
> > lib/hash/rte_cuckoo_hash.c | 9 +++++++++
> > lib/hash/rte_hash.h | 13 +++++++++++++
> > lib/hash/version.map | 1 +
> > lib/rcu/rte_rcu_qsbr.c | 8 ++++++++
> > lib/rcu/rte_rcu_qsbr.h | 11 +++++++++++
> > lib/rcu/version.map | 1 +
> > 6 files changed, 43 insertions(+)
> >
> > diff --git a/lib/hash/rte_cuckoo_hash.c b/lib/hash/rte_cuckoo_hash.c
> > index 70456754c4..3553f3efc7 100644
> > --- a/lib/hash/rte_cuckoo_hash.c
> > +++ b/lib/hash/rte_cuckoo_hash.c
> > @@ -555,6 +555,15 @@ rte_hash_max_key_id(const struct rte_hash *h)
> > return h->entries;
> > }
> >
> > +int32_t
> > +rte_hash_dq_count(const struct rte_hash *h)
> > +{
> > + if (h->dq == NULL)
> input arguments must be checked since this is a public API, the same is
> true for rte_rcu_qsbr_dq_count()
> > + return -EINVAL;
> why not just return 0?
> > +
> > + return rte_rcu_qsbr_dq_count(h->dq);
> > +}
> > +
> > int32_t
> > rte_hash_count(const struct rte_hash *h)
> > {
> > diff --git a/lib/hash/rte_hash.h b/lib/hash/rte_hash.h
> > index 7ecc021111..8ea97e297d 100644
> > --- a/lib/hash/rte_hash.h
> > +++ b/lib/hash/rte_hash.h
> > @@ -193,6 +193,19 @@ rte_hash_free(struct rte_hash *h);
> > void
> > rte_hash_reset(struct rte_hash *h);
> >
> > +
> > +/**
> > + * Return the number of records in the defer queue of the hash table
> > + * if RCU is enabled.
> > + * @param h
> > + * Hash table to query from
> > + * @return
> > + * - -EINVAL if parameters are invalid
> > + * - A value indicating how many records were inserted in the table.
> did you mean how many records are kept in defer queue?
> > + */
> > +int32_t
> > +rte_hash_dq_count(const struct rte_hash *h);
> > +
> > /**
> > * Return the number of keys in the hash table
> > * @param h
> > diff --git a/lib/hash/version.map b/lib/hash/version.map
> > index 6b2afebf6b..7f7b158cf1 100644
> > --- a/lib/hash/version.map
> > +++ b/lib/hash/version.map
> > @@ -9,6 +9,7 @@ DPDK_24 {
> > rte_hash_add_key_with_hash;
> > rte_hash_add_key_with_hash_data;
> > rte_hash_count;
> > + rte_hash_dq_count;
> new API must introduced as an experimental API. The same is true for
> rte_rcu_qsbr_dq_count()
> > rte_hash_crc32_alg;
> > rte_hash_crc_set_alg;
> > rte_hash_create;
> > diff --git a/lib/rcu/rte_rcu_qsbr.c b/lib/rcu/rte_rcu_qsbr.c
> > index bd0b83be0c..89f8da4c4c 100644
> > --- a/lib/rcu/rte_rcu_qsbr.c
> > +++ b/lib/rcu/rte_rcu_qsbr.c
> > @@ -450,6 +450,14 @@ rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq,
> > unsigned int n,
> > return 0;
> > }
> >
> > +/**
> > + * Return the number of entries in a defer queue.
> > + */
> > +unsigned int rte_rcu_qsbr_dq_count(struct rte_rcu_qsbr_dq *dq)
> > +{
Please validate dq here.
> > + return rte_ring_count(dq->r);
> > +}
> > +
> > /* Delete a defer queue. */
> > int
> > rte_rcu_qsbr_dq_delete(struct rte_rcu_qsbr_dq *dq)
> > diff --git a/lib/rcu/rte_rcu_qsbr.h b/lib/rcu/rte_rcu_qsbr.h
> > index 23c9f89805..ed5a590edd 100644
> > --- a/lib/rcu/rte_rcu_qsbr.h
> > +++ b/lib/rcu/rte_rcu_qsbr.h
> > @@ -794,6 +794,17 @@ int
> > rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq, unsigned int n,
> > unsigned int *freed, unsigned int *pending, unsigned int *available);
> >
> > +/**
> > + * Return the number of entries in a defer queue.
> > + *
> > + * @param dq
> > + * Defer queue.
> > + * @return
> > + * The number of entries in the defer queue.
> > + */
> > +unsigned int
> > +rte_rcu_qsbr_dq_count(struct rte_rcu_qsbr_dq *dq);
Agree on the need for this API in RCU
> > +
> > /**
> > * Delete a defer queue.
> > *
> > diff --git a/lib/rcu/version.map b/lib/rcu/version.map
> > index 982ffd59d9..f410ab41e7 100644
> > --- a/lib/rcu/version.map
> > +++ b/lib/rcu/version.map
> > @@ -5,6 +5,7 @@ DPDK_24 {
> > rte_rcu_qsbr_dq_create;
> > rte_rcu_qsbr_dq_delete;
> > rte_rcu_qsbr_dq_enqueue;
> > + rte_rcu_qsbr_dq_count;
> > rte_rcu_qsbr_dq_reclaim;
> > rte_rcu_qsbr_dump;
> > rte_rcu_qsbr_get_memsize;
>
> --
> Regards,
> Vladimir
>
