Hi Bruce/Pablo,
I need to get this into 18.11, appreciate any review/feedback soon.
Thank you,
Honnappa
> -----Original Message-----
> From: Honnappa Nagarahalli
> Sent: Friday, September 14, 2018 4:19 PM
> To: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>;
> bruce.richard...@intel.com; pablo.de.lara.gua...@intel.com
> Cc: dev@dpdk.org; honnappa.nagarahalli; Gavin Hu (Arm Technology China)
> <gavin...@arm.com>; Steve Capper <steve.cap...@arm.com>; Ola Liljedahl
> <ola.liljed...@arm.com>; nd <n...@arm.com>; yipeng1.w...@intel.com;
> Michel Machado <mic...@digirati.com.br>; sameh.gobr...@intel.com
> Subject: RE: [PATCH 0/4] Address reader-writer concurrency in rte_hash
>
> I have added the memory ordering ladder diagrams to the DPDK summit slides
> to help understand the changes. The slides are available at:
> https://dpdkuserspace2018.sched.com/event/G44w/lock-free-read-write-
> concurrency-in-rtehash. Please look at the backup slides.
>
> Thank you,
> Honnappa
>
> -----Original Message-----
> From: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Sent: Thursday, September 6, 2018 12:12 PM
> To: bruce.richard...@intel.com; pablo.de.lara.gua...@intel.com
> Cc: dev@dpdk.org; honnappa.nagarahalli; Gavin Hu (Arm Technology China)
> <gavin...@arm.com>; Steve Capper <steve.cap...@arm.com>; Ola Liljedahl
> <ola.liljed...@arm.com>; nd <n...@arm.com>; Honnappa Nagarahalli
> <honnappa.nagaraha...@arm.com>
> Subject: [PATCH 0/4] Address reader-writer concurrency in rte_hash
>
> Currently, reader-writer concurrency problems in rte_hash are
> addressed using reader-writer locks. Use of reader-writer locks
> results in following issues:
>
> 1) In many of the use cases for the hash table, writer threads
> are running on control plane. If the writer is preempted while
> holding the lock, it will block the readers for an extended period
> resulting in packet drops. This problem seems to apply for platforms
> with transactional memory support as well because of the algorithm
> used for rte_rwlock_write_lock_tm:
>
> static inline void
> rte_rwlock_write_lock_tm(rte_rwlock_t *rwl)
> {
> if (likely(rte_try_tm(&rwl->cnt)))
> return;
> rte_rwlock_write_lock(rwl);
> }
>
> i.e. there is a posibility of using rte_rwlock_write_lock in
> failure cases.
> 2) Reader-writer lock based solution does not address the following
> issue.
> rte_hash_lookup_xxx APIs return the index of the element in
> the key store. Application(reader) can use that index to reference
> other data structures in its scope. Because of this, the
> index should not be freed till the application completes
> using the index.
> 3) Since writer blocks all the readers, the hash lookup
> rate comes down significantly when there is activity on the writer.
> This happens even for unrelated entries. Performance numbers
> given below clearly indicate this.
>
> Lock-free solution is required to solve these problems. This patch
> series adds the lock-free capabilities in the following steps:
>
> 1) Correct the alignment for the key store entry to prep for
> memory ordering.
> 2) Add memory ordering to prevent race conditions when a new key
> is added to the table.
>
> 3) Reader-writer concurrency issue, caused by moving the keys
> to their alternate locations during key insert, is solved
> by introducing an atomic global counter indicating a change
> in table.
>
> 4) This solution also has to solve the issue of readers using
> key store element even after the key is deleted from
> control plane.
> To solve this issue, the hash_del_key_xxx APIs do not free
> the key store element. The key store element has to be freed
> using the newly introduced rte_hash_free_key_with_position API.
> It needs to be called once all the readers have stopped using
> the key store element. How this is determined is outside
> the scope of this patch (RCU is one such mechanism that the
> application can use).
>
> 4) Finally, a lock free reader-writer concurrency flag is added
> to enable this feature at run time.
>
> Performance numbers:
> Scenario: Equal number of writer/reader threads for concurrent
> writers and readers. For readers only test, the
> entries are added upfront.
>
> Current code:
> Cores Lookup Lookup
> with add
> 2 474 246
> 4 935 579
> 6 1387 1048
> 8 1766 1480
> 10 2119 1951
> 12 2546 2441
>
> With this patch:
> Cores Lookup Lookup
> with add
> 2 291 211
> 4 297 196
> 6 304 198
> 8 309 202
> 10 315 205
> 12 319 209
>
> Honnappa Nagarahalli (4):
> hash: correct key store element alignment
> hash: add memory ordering to avoid race conditions
> hash: fix rw concurrency while moving keys
> hash: enable lock-free reader-writer concurrency
>
> lib/librte_hash/rte_cuckoo_hash.c | 445 +++++++++++++++++++++++++-------
> ---
> lib/librte_hash/rte_cuckoo_hash.h | 6 +-
> lib/librte_hash/rte_hash.h | 63 ++++-
> lib/librte_hash/rte_hash_version.map | 7 +
> 4 files changed, 393 insertions(+), 128 deletions(-)
>
> --
> 2.7.4
