From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id 005A0A0487 for ; Thu, 4 Jul 2019 02:39:19 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 3CEF41E20; Thu, 4 Jul 2019 02:39:18 +0200 (CEST) Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by dpdk.org (Postfix) with ESMTP id A05A51D9E; Thu, 4 Jul 2019 02:39:15 +0200 (CEST) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Jul 2019 17:39:14 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,449,1557212400"; d="scan'208";a="363205362" Received: from orsmsx104.amr.corp.intel.com ([10.22.225.131]) by fmsmga006.fm.intel.com with ESMTP; 03 Jul 2019 17:39:13 -0700 Received: from orsmsx156.amr.corp.intel.com (10.22.240.22) by ORSMSX104.amr.corp.intel.com (10.22.225.131) with Microsoft SMTP Server (TLS) id 14.3.439.0; Wed, 3 Jul 2019 17:39:13 -0700 Received: from orsmsx104.amr.corp.intel.com ([169.254.4.70]) by ORSMSX156.amr.corp.intel.com ([169.254.8.198]) with mapi id 14.03.0439.000; Wed, 3 Jul 2019 17:39:13 -0700 From: "Wang, Yipeng1" To: Honnappa Nagarahalli , "Gobriel, Sameh" , "Richardson, Bruce" , "De Lara Guarch, Pablo" CC: "Gavin Hu (Arm Technology China)" , "Ruifeng Wang (Arm Technology China)" , "dev@dpdk.org" , nd , "stable@dpdk.org" , nd Thread-Topic: [PATCH 2/3] lib/hash: load pData after full key compare Thread-Index: AQHVK5syNdL2m0zXvEuHE2Sc2GqGyKaxYNTwgAXcXYCAAmsW8A== Date: Thu, 4 Jul 2019 00:39:12 +0000 Message-ID: References: <20190625211520.43181-1-honnappa.nagarahalli@arm.com> <20190625211520.43181-3-honnappa.nagarahalli@arm.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-product: dlpe-windows dlp-version: 11.0.600.7 dlp-reaction: no-action x-ctpclassification: CTP_NT x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiNDc0OGQ4MzItMTAxZC00OWM5LWIwOTgtZDQzYTZlNjM5YzZhIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE3LjEwLjE4MDQuNDkiLCJUcnVzdGVkTGFiZWxIYXNoIjoiRG8zVG02cGNPQ0htNDliUWN5QnNcL2liVDBDN0VqK1N5SzM2dmxDS2Q0TnU2NE1PYngwYUZJMGtXOFpsUmo1eEEifQ== x-originating-ip: [10.22.254.140] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [dpdk-dev] [PATCH 2/3] lib/hash: load pData after full key compare 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" >-----Original Message----- >From: Honnappa Nagarahalli [mailto:Honnappa.Nagarahalli@arm.com] >Sent: Monday, July 1, 2019 9:35 PM >To: Wang, Yipeng1 ; Gobriel, Sameh ; Richardson, Bruce >; De Lara Guarch, Pablo >Cc: Gavin Hu (Arm Technology China) ; Ruifeng Wang (Arm = Technology China) ; >dev@dpdk.org; Honnappa Nagarahalli ; nd ; stable@dpdk.org; nd >Subject: RE: [PATCH 2/3] lib/hash: load pData after full key compare > >Thank you Yipeng for your comments. > >> > >> >When a hash entry is added, there are 2 sets of stores. >> > >> >1) The application writes its data to memory (whose address is provided >> >in rte_hash_add_key_with_hash_data API (or NULL)) >> >2) The rte_hash library writes to its own internal data structures; key >> >store entry and the hash table. >> > >> >The only ordering requirement between these 2 is that - the store to >> >the application data must complete before the store to key_index. >> >There are no ordering requirements between the stores to the >> >key/signature and store to application data. The synchronization point >> >for application data can be any point between the 'store to application >> >data' and 'store to the key_index'. So, pData should not be a guard >> >variable for the data in hash table. It should be a guard variable only >> >for the application data written to the memory location pointed by >> >pData. Hence, pData can be loaded after full key comparison. >> > >> >Fixes: e605a1d36 ("hash: add lock-free r/w concurrency") >> >Cc: stable@dpdk.org >> > >> >Signed-off-by: Honnappa Nagarahalli >> >Reviewed-by: Gavin Hu >> >Tested-by: Ruifeng Wang >> >--- >> > lib/librte_hash/rte_cuckoo_hash.c | 67 +++++++++++++++---------------- >> > 1 file changed, 32 insertions(+), 35 deletions(-) >> > >> >diff --git a/lib/librte_hash/rte_cuckoo_hash.c >> >b/lib/librte_hash/rte_cuckoo_hash.c >> >index f37f6957d..077328fed 100644 >> >--- a/lib/librte_hash/rte_cuckoo_hash.c >> >+++ b/lib/librte_hash/rte_cuckoo_hash.c >> >@@ -649,9 +649,11 @@ search_and_update(const struct rte_hash *h, void >> *data, const void *key, >> > k =3D (struct rte_hash_key *) ((char *)keys + >> > bkt->key_idx[i] * h->key_entry_size); >> > if (rte_hash_cmp_eq(key, k->key, h) =3D=3D 0) { >> >- /* 'pdata' acts as the synchronization point >> >- * when an existing hash entry is updated. >> >- * Key is not updated in this case. >> >+ /* The store to application data at *data >> >+ * should not leak after the store to pdata >> >+ * in the key store. i.e. pdata is the guard >> >+ * variable. Release the application data >> >+ * to the readers. >> > */ >> > __atomic_store_n(&k->pdata, >> > data, >> >@@ -711,11 +713,10 @@ rte_hash_cuckoo_insert_mw(const struct >> rte_hash *h, >> > /* Check if slot is available */ >> > if (likely(prim_bkt->key_idx[i] =3D=3D EMPTY_SLOT)) { >> > prim_bkt->sig_current[i] =3D sig; >> >- /* Key can be of arbitrary length, so it is >> >- * not possible to store it atomically. >> >- * Hence the new key element's memory stores >> >- * (key as well as data) should be complete >> >- * before it is referenced. >> >+ /* Store to signature and key should not >> >+ * leak after the store to key_idx. i.e. >> >+ * key_idx is the guard variable for signature >> >+ * and key. >> > */ >> > __atomic_store_n(&prim_bkt->key_idx[i], >> > new_idx, >> >@@ -990,17 +991,15 @@ __rte_hash_add_key_with_hash(const struct >> >rte_hash *h, const void *key, >> > >> > new_k =3D RTE_PTR_ADD(keys, (uintptr_t)slot_id * h->key_entry_size); >> > new_idx =3D (uint32_t)((uintptr_t) slot_id); >> >- /* Copy key */ >> >- memcpy(new_k->key, key, h->key_len); >> >- /* Key can be of arbitrary length, so it is not possible to store >> >- * it atomically. Hence the new key element's memory stores >> >- * (key as well as data) should be complete before it is referenced. >> >- * 'pdata' acts as the synchronization point when an existing hash >> >- * entry is updated. >> >+ /* The store to application data (by the application) at *data should >> >+ * not leak after the store of pdata in the key store. i.e. pdata is >> >+ * the guard variable. Release the application data to the readers. >> > */ >> > __atomic_store_n(&new_k->pdata, >> > data, >> > __ATOMIC_RELEASE); >> [Wang, Yipeng] Actually do we need to guard pdata for the newly inserted >> key? I thought the guard of key_idx already can make sure The order for= the >> application to read data. >Yes, you are correct. In the hash_add case, the store-release on key_idx w= ould be sufficient. However, hash_update case requires >store-release on pData. This was the reason to keep store-release for pDat= a in hash_add when the lock-free algorithm was >introduced. [Wang, Yipeng] Sorry that I am still a bit confused, we already have store = release in search_and_update function right? Isn't that enough for the hash_update case? > >> >+ /* Copy key */ >> >+ memcpy(new_k->key, key, h->key_len); >> [Wang, Yipeng] You don't need to do the order change just to show the po= int >> of unnecessary ordering I think. >> I am afraid it may cause further confusion for future people who read th= is >> change, especially it is not in the commit Message (and it is a bug fix)= . >I made this change to keep it inline with the corresponding change in the = lookup function. I can add this explanation to the commit >message. Please let me know if this is ok for you. [Wang, Yipeng] Thanks for the change. To me it still looks unnecessary but If you think this cosmetic change woul= d help others to understand the code better, I am OK with it.