From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by dpdk.org (Postfix) with ESMTP id 4994E1B396 for ; Wed, 3 Oct 2018 20:00:19 +0200 (CEST) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Oct 2018 11:00:18 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,336,1534834800"; d="scan'208";a="94350044" Received: from fmsmsx103.amr.corp.intel.com ([10.18.124.201]) by fmsmga004.fm.intel.com with ESMTP; 03 Oct 2018 10:56:32 -0700 Received: from fmsmsx115.amr.corp.intel.com (10.18.116.19) by FMSMSX103.amr.corp.intel.com (10.18.124.201) with Microsoft SMTP Server (TLS) id 14.3.319.2; Wed, 3 Oct 2018 10:56:32 -0700 Received: from fmsmsx151.amr.corp.intel.com ([169.254.7.87]) by fmsmsx115.amr.corp.intel.com ([169.254.4.9]) with mapi id 14.03.0319.002; Wed, 3 Oct 2018 10:56:32 -0700 From: "Wang, Yipeng1" To: Honnappa Nagarahalli , "Van Haaren, Harry" , "Richardson, Bruce" CC: "De Lara Guarch, Pablo" , "dev@dpdk.org" , "Gavin Hu (Arm Technology China)" , "Steve Capper" , Ola Liljedahl , nd , "Gobriel, Sameh" Thread-Topic: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys Thread-Index: AQHUVwkACltYuMWFq0OFAy/59/n9TqUJ4m0AgAKJQACAAD1o4IABnHOA//+PSkA= Date: Wed, 3 Oct 2018 17:56:31 +0000 Message-ID: References: <1536253938-192391-1-git-send-email-honnappa.nagarahalli@arm.com> <1536253938-192391-4-git-send-email-honnappa.nagarahalli@arm.com> <20180928082610.GA7592@bricha3-MOBL.ger.corp.intel.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: 11.0.400.15 dlp-reaction: no-action x-ctpclassification: CTP_NT x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiMTFjODExOTgtZjM2Yy00Yzc2LWJiZmMtZDZhOTM3MGY1NmE5IiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE3LjEwLjE4MDQuNDkiLCJUcnVzdGVkTGFiZWxIYXNoIjoiQmtjNFFiVHRZOTVweEg5T1RNT2s5NFVlTkt3SXdBZDV1bG9xSlpVOGVCQ040UFdwZXFtN2tQOStoZW1jWG1UayJ9 x-originating-ip: [10.1.200.107] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys 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: , X-List-Received-Date: Wed, 03 Oct 2018 18:00:20 -0000 >-----Original Message----- >From: Honnappa Nagarahalli [mailto:Honnappa.Nagarahalli@arm.com] >Sent: Wednesday, October 3, 2018 10:33 AM >To: Wang, Yipeng1 ; Van Haaren, Harry ; Richardson, Bruce > >Cc: De Lara Guarch, Pablo ; dev@dpdk.org; = Gavin Hu (Arm Technology China) >; Steve Capper ; Ola Liljedahl ; nd ; Gobriel, >Sameh >Subject: RE: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving = keys > >> >-----Original Message----- >> >From: Van Haaren, Harry >> >> > > > > /** >> >> > > > > * Add a key to an existing hash table. >> >> > > > >@@ -222,7 +222,7 @@ rte_hash_add_key(const struct rte_hash *h, >> >> > > > >const void >> >> > > *key); >> >> > > > > * array of user data. This value is unique for this key. >> >> > > > > */ >> >> > > > > int32_t >> >> > > > >-rte_hash_add_key_with_hash(const struct rte_hash *h, const >> >> > > > >void *key, >> >> > > hash_sig_t sig); >> >> > > > >+rte_hash_add_key_with_hash(struct rte_hash *h, const void >> >> > > > >+*key, >> >> > > hash_sig_t sig); >> >> > > > > >> >> > > > > / >> >> > > > >> >> > > > I think the above changes will break ABI by changing the >> >> > > > parameter >> >> type? >> >> > > Other people may know better on this. >> >> > > >> >> > > Just removing a const should not change the ABI, I believe, since >> >> > > the const is just advisory hint to the compiler. Actual parameter >> >> > > size and count remains unchanged so I don't believe there is an i= ssue. >> >> > > [ABI experts, please correct me if I'm wrong on this] >> >> > >> >> > >> >> > [Certainly no ABI expert, but...] >> >> > >> >> > I think this is an API break, not ABI break. >> >> > >> >> > Given application code as follows, it will fail to compile - even >> >> > though >> >> running >> >> > the new code as a .so wouldn't cause any issues (AFAIK). >> >> > >> >> > void do_hash_stuff(const struct rte_hash *h, ...) { >> >> > /* parameter passed in is const, but updated function prototype >> >> > is >> >> non- >> >> > const */ >> >> > rte_hash_add_key_with_hash(h, ...); } >> >> > >> >> > This means that we can't recompile apps against latest patch >> >> > without application code changes, if the app was passing a const >> >> > rte_hash struct >> >> as >> >> > the first parameter. >> >> > >> >> Agree. Do we need to do anything for this? >> > >> >I think we should try to avoid breaking API wherever possible. >> >If we must, then I suppose we could follow the ABI process of a >> >deprecation notice. >> > >> >From my reading of the versioning docs, it doesn't document this case: >> >https://doc.dpdk.org/guides/contributing/versioning.html >> > >> >I don't recall a similar situation in DPDK previously - so I suggest >> >you ask Tech board for input here. >> > >> >Hope that helps! -Harry >> [Wang, Yipeng] >> Honnappa, how about use a pointer to the counter in the rte_hash struct >> instead of the counter? Will this avoid API change? >I think it defeats the purpose of 'const' parameter to the API and provide= s incorrect information to the user. >IMO, DPDK should have guidelines on how to handle the API compatibility br= eaks. I will send an email to tech board on this. >We can also solve this by having counters on the bucket. I was planning to= do this little bit later. I will look at the effort involved and >may be do it now. [Wang, Yipeng]=20 I think with ABI/API change, you might need to announce it one release cycl= e ahead. In the cuckoo switch paper: Scalable, High Performance Ethernet Forwarding = with CUCKOOSWITCH it separates the version counter array and the hash table. You can strike a= balance between granularity of the version counter and the cache/memory requirement= . Is it a better way? Another consideration is current bucket is 64-byte exactly with the partial= -key-hashing. To add another counter, we need to think about changing certain variables t= o still align cache line.