On Fri, Sep 28, 2018 at 02:00:00AM +0100, Wang, Yipeng1 wrote: > 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.
Just removing a const should not change the ABI, I believe, since the const is just advisory hint to the compiler. Actual parameter size and count remains unchanged so I don't believe there is an issue. [ABI experts, please correct me if I'm wrong on this] /Bruce
