<snip> > On Wed, 6 Jul 2022 19:07:54 +0530 > venkatesh bs <venki....@gmail.com> wrote: > > > Hi All, > > > > In multithreaded/Multicore environment can we use > > RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF > > independently, This flag is about reader-writer concurrency (not writer-writer concurrency). Reader-writer concurrency will use lock-free algorithm allowing for the data plane to scale well.
> > or this flag should always be used with > > RTE_HASH_EXTRA_FLAGS_MULTI_WRITER_ADD. If you have multiple writers, you need to enable this flag. This is unrelated to RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF. > > > > We are trying to create and access the hash table with > > RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF > > only. > > We are getting crashes in multi core environments , we debugged > > nothing wrong in the application , everything looks good. If the crash is happening while adding/deleting keys and there are multiple writers, enabling RTE_HASH_EXTRA_FLAGS_MULTI_WRITER_ADD might solve the problem. > > > > We call rte_hash_del_key() first and from the returned position we are > > calling rte_hash_free_key_with_position(). > > > > Please let me know if we missed something. > > > > Thanks, > > Venkatesh. > > Repeating same question doesn't get answer faster. > > Read the code, it is fairly straightforward. > > The multi-writer add means that writers take a lock. > If doing lock free support then: > 1. It is up to your application to use a single writer and/or > wrap writer calls in a lock. > > 2. You need to use RCU mechanism to guarantee that no reader > will access a deleted entry. Something like: > > rte_hash_del_key() > synchronize_rcu() > rte_hash_free_key_with_position() > > You can use either the DPDK RCU library or the userspace RCU library. > Read that documentation, RCU is non-trivial change. RCU is integrated in the hash library. You could use that as well. Look at ' rte_hash_rcu_qsbr_add' API for more details. >
