> >> > > >> >Add the flag to enable reader-writer concurrency during run time. > >> >The rte_hash_del_xxx APIs do not free the keystore element when this > >> >flag is enabled. Hence a new API, rte_hash_free_key_with_position, > >> >to free the key store element is added. > >> > > >> >+/** Flag to support lock free reader writer concurrency */ #define > >> >+RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF 0x08 > >> [Wang, Yipeng] It would be good to indicate that the lockless > >> implementation works for single writer multiple readers. > >Multi-writers are supported by using the rw-lock or transactional > >memory. Essentially, we still have single writer. This patch works fine with > multi-writer as defined by ' MULTI_WRITER_ADD' flag. I have tested it as well. > I will enable this test case in V2. > > > >> Also, if people use a mix of the flags for example set both > >> multiwriter and LF flags, then I guess either we need to return an > >> error or maybe multiwriter should have higher priority. Currently the > >> RW_CONCURRENCY will assume MULTI_WRITER_ADD I think. > >As mentioned above, multi-writer and LF combination is supported. Yes, > RW_CONCURRENCY currently assumes MULTI_WRITER_ADD. > >I think we should separate them. > [Wang, Yipeng] It would be great if you could just add a little bit more > comments to both of the flags to be more specific on what Read write > concurrency mean in both cases, just in case users got confused. > You may also want to update the documentation later > (https://doc.dpdk.org/guides/prog_guide/hash_lib.html). I will add the documentation once the patch is accepted.
> > > > >> >+ > >> > /** Signature of key that is stored internally. */ typedef uint32_t > >> > hash_sig_t; > >> > > >> >@@ -143,6 +148,11 @@ rte_hash_count(const struct rte_hash *h); > >> > * and should only be called from one thread by default. > >> > * Thread safety can be enabled by setting flag during > >> > * table creation. > >> >+ * When lock free reader writer concurrency is enabled, > >> >+ * if this API is called to update an existing entry, > >> >+ * the application should free any memory allocated for > >> >+ * previous 'data' only after all the readers have stopped > >> >+ * using previous 'data'. > >> [Wang, Yipeng] Could you be more specific on this description? > >> When add_key API is called, the users do not know if it will update > >> an existing entry or inserting a new one, do they? > >I think, it will depend on the application. The applications I have > >worked on so far, added a hash entry as a result of receiving an event > >and updated it on receiving another event. I can change the comments to > indicate that the applications need to be aware of add/update operations. > [Wang, Yipeng] Even if for current rte_hash, after update, the application may > still use the old data. It is the upper level application's Responsibility. > How is it > specific to lock free implementation? I agree. I think it makes sense to keep this warning, but make it not specific to lock-free algorithm. I will make this change in V3. > > > >> > rte_hash_del_key(const struct rte_hash *h, const void *key); @@ > >> > -251,6 > >> >+274,12 @@ rte_hash_del_key(const struct rte_hash *h, const void > >> >+*key); > >> > * and should only be called from one thread by default. > >> > * Thread safety can be enabled by setting flag during > >> > * table creation. > >> >+ * If lock free reader writer concurrency is enabled, > >> >+ * the hash library's internal memory for the deleted > >> >+ * key is not freed. It should be freed by calling > >> >+ * rte_hash_free_key_with_position API after all > >> >+ * the readers have stopped using the hash entry > >> >+ * corresponding to this key. > >> > * > >> > * @param h > >> > * Hash table to remove the key from. > >> >@@ -264,6 +293,8 @@ rte_hash_del_key(const struct rte_hash *h, const > >> void *key); > >> > * - A positive value that can be used by the caller as an offset into > >> > an > >> > * array of user data. This value is unique for this key, and is the > >> > same > >> > * value that was returned when the key was added. > >> >+ * When lock free concurrency is enabled, this value should be used > >> >+ * while calling the rte_hash_free_key_with_position API. > >> > */ > >> > int32_t > >> > rte_hash_del_key_with_hash(const struct rte_hash *h, const void > >> >*key, hash_sig_t sig); @@ -290,6 +321,30 @@ > >> rte_hash_get_key_with_position(const struct rte_hash *h, const > >> int32_t position, > >> > void **key); > >> > > >> [Wang, Yipeng] If possible, how about having a new delete function > >> instead of modifying the current one? > >> I think it does not need to be tied with the lockless implementation, > >> it is orthogonal to multi-threading implementation. > >> people using locks may still want this new deletion behavior. > >> If people want old behavior, they can call current API, otherwise > >> they can call the new deletion function, followed by > Rte_hash_free_key_with_position later. > >I like the terms 'delete' and 'free'. I am finding it hard to come up > >with a good name for the API. It will be on the lines of > 'rte_hash_del_key_with_hash_no_free' - I do not like the name much. > >Instead, we could have a configuration flag for the hash table, > >'RTE_HASH_EXTRA_FLAGS_FREE_MEM_ON_DEL'. If this is enabled, > 'rte_hash_del_...' APIs will free the key store index and any internal memory. > Enabling lock-free RW concurrency will enable this flag. > >User can enable this flag explicitly while not using lock-free RW concurrency > as well. > [Wang, Yipeng] I am OK with either way. For flag, maybe we should call it > RTE_HASH_EXTRA_FLAGS_RECYCLE _ON_DEL, since The key-data pair index is > recycled to be more specific. User should know that the index might be re- > used by another write. > BTW, current flag is only 8 bit, as we specify more and more flags, maybe we > should announce an API change to change it to 32bit for next release. I agree. Do you know how to do this? Do you want to take care of this?
