From patchwork Thu Oct 11 04:59:25 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Honnappa Nagarahalli X-Patchwork-Id: 46535 Return-Path: X-Original-To: patchwork@dpdk.org Delivered-To: patchwork@dpdk.org Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 49B0E1B1FB; Thu, 11 Oct 2018 06:59:43 +0200 (CEST) Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by dpdk.org (Postfix) with ESMTP id 57F645F13 for ; Thu, 11 Oct 2018 06:59:42 +0200 (CEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 426A37A9; Wed, 10 Oct 2018 21:59:41 -0700 (PDT) Received: from 2p2660v4-1.austin.arm.com (2p2660v4-1.austin.arm.com [10.118.12.190]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D9ECB3F5B3; Wed, 10 Oct 2018 21:59:40 -0700 (PDT) From: Honnappa Nagarahalli To: bruce.richardson@intel.com, pablo.de.lara.guarch@intel.com Cc: dev@dpdk.org, yipeng1.wang@intel.com, honnappa.nagarahalli@arm.com, Dharmik.Thakkar@arm.com, nd@arm.com Date: Wed, 10 Oct 2018 23:59:25 -0500 Message-Id: <1539233972-49860-1-git-send-email-honnappa.nagarahalli@arm.com> X-Mailer: git-send-email 2.7.4 Subject: [dpdk-dev] [PATCH v2 0/7] Address reader-writer concurrency in rte_hash X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 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) Add support to not free the key-store index upon calling rte_hash_del_xxx APIs. This solves the issue in 2). 2) Correct the alignment for the key store entry to prep for memory ordering. 3) Add memory ordering to prevent race conditions when a new key is added to the table. 4) 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. 5) 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 when lock-free algorithm is enabled. 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). 6) Finally, a lock free reader-writer concurrency flag is added to enable this feature at run time. Performance numbers can be got from the additional test case added as part of this patch. v1->v2 1) Separate multi-writer capability from rw concurrency 2) Add do not recycle on delete feature (Yipeng) 3) Add Arm copyright 4) Add test case to test lock-free algorithm and multi-writer test case (Yipeng) 5) Additional API documentation to indicate RCU usage (Yipeng) 6) Additional documentation on rte_hash_reset API (Yipeng) 7) Allocate memory for the global counter and avoid API changes (Yipeng) Dharmik Thakkar (1): test/hash: read-write lock-free concurrency test Honnappa Nagarahalli (6): hash: separate multi-writer from rw-concurrency hash: support do not recycle on delete 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 | 483 +++++++++++---- lib/librte_hash/rte_cuckoo_hash.h | 17 +- lib/librte_hash/rte_hash.h | 82 ++- lib/librte_hash/rte_hash_version.map | 7 + test/test/Makefile | 1 + test/test/meson.build | 1 + test/test/test_hash.c | 140 ++++- test/test/test_hash_readwrite.c | 6 +- test/test/test_hash_readwrite_lf.c | 1084 ++++++++++++++++++++++++++++++++++ 9 files changed, 1686 insertions(+), 135 deletions(-) create mode 100644 test/test/test_hash_readwrite_lf.c