Reply inlined:
>-----Original Message-----
>From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Honnappa Nagarahalli
>Sent: Thursday, September 6, 2018 10:12 AM
>To: Richardson, Bruce <bruce.richard...@intel.com>; De Lara Guarch, Pablo
><pablo.de.lara.gua...@intel.com>
>Cc: dev@dpdk.org; honnappa.nagaraha...@dpdk.org; gavin...@arm.com;
>steve.cap...@arm.com; ola.liljed...@arm.com;
>n...@arm.com; Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
>Subject: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys
>
>Reader-writer concurrency issue, caused by moving the keys
>to their alternative locations during key insert, is solved
>by introducing a global counter(tbl_chng_cnt) indicating a
>change in table.
>
>@@ -662,6 +679,20 @@ rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
> curr_bkt = curr_node->bkt;
> }
>
>+ /* Inform the previous move. The current move need
>+ * not be informed now as the current bucket entry
>+ * is present in both primary and secondary.
>+ * Since there is one writer, load acquires on
>+ * tbl_chng_cnt are not required.
>+ */
>+ __atomic_store_n(&h->tbl_chng_cnt,
>+ h->tbl_chng_cnt + 1,
>+ __ATOMIC_RELEASE);
>+ /* The stores to sig_alt and sig_current should not
>+ * move above the store to tbl_chng_cnt.
>+ */
>+ __atomic_thread_fence(__ATOMIC_RELEASE);
>+
[Wang, Yipeng] I believe for X86 this fence should not be compiled to any code,
otherwise
we need macros for the compile time check.
>@@ -926,30 +957,56 @@ __rte_hash_lookup_with_hash(const struct rte_hash *h,
>const void *key,
> uint32_t bucket_idx;
> hash_sig_t alt_hash;
> struct rte_hash_bucket *bkt;
>+ uint32_t cnt_b, cnt_a;
> int ret;
>
>- bucket_idx = sig & h->bucket_bitmask;
>- bkt = &h->buckets[bucket_idx];
>-
> __hash_rw_reader_lock(h);
>
>- /* Check if key is in primary location */
>- ret = search_one_bucket(h, key, sig, data, bkt);
>- if (ret != -1) {
>- __hash_rw_reader_unlock(h);
>- return ret;
>- }
>- /* Calculate secondary hash */
>- alt_hash = rte_hash_secondary_hash(sig);
>- bucket_idx = alt_hash & h->bucket_bitmask;
>- bkt = &h->buckets[bucket_idx];
>+ do {
[Wang, Yipeng] As far as I know, the MemC3 paper "MemC3: Compact and Concurrent
MemCache with Dumber Caching and Smarter Hashing"
as well as OvS cmap uses similar version counter to implement read-write
concurrency for hash table,
but one difference is reader checks even/odd of the version counter to make
sure there is no
concurrent writer. Could you just double check and confirm that this is not
needed for your implementation?
>--- a/lib/librte_hash/rte_hash.h
>+++ b/lib/librte_hash/rte_hash.h
>@@ -156,7 +156,7 @@ rte_hash_count(const struct rte_hash *h);
> * - -ENOSPC if there is no space in the hash for this key.
> */
> int
>-rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data);
>+rte_hash_add_key_data(struct rte_hash *h, const void *key, void *data);
>
> /**
> * Add a key-value pair with a pre-computed hash value
>@@ -180,7 +180,7 @@ rte_hash_add_key_data(const struct rte_hash *h, const void
>*key, void *data);
> * - -ENOSPC if there is no space in the hash for this key.
> */
> int32_t
>-rte_hash_add_key_with_hash_data(const struct rte_hash *h, const void *key,
>+rte_hash_add_key_with_hash_data(struct rte_hash *h, const void *key,
> hash_sig_t sig, void *data);
>
> /**
>@@ -200,7 +200,7 @@ rte_hash_add_key_with_hash_data(const struct rte_hash *h,
>const void *key,
> * array of user data. This value is unique for this key.
> */
> int32_t
>-rte_hash_add_key(const struct rte_hash *h, const void *key);
>+rte_hash_add_key(struct rte_hash *h, const void *key);
>
> /**
> * Add a key to an existing hash table.
>@@ -222,7 +222,7 @@ rte_hash_add_key(const struct rte_hash *h, const void
>*key);
> * array of user data. This value is unique for this key.
> */
> int32_t
>-rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
>hash_sig_t sig);
>+rte_hash_add_key_with_hash(struct rte_hash *h, const void *key, hash_sig_t
>sig);
>
> /
I think the above changes will break ABI by changing the parameter type? Other
people may know better on this.
