From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id CDDF15B3E for ; Mon, 21 Jan 2019 15:14:43 +0100 (CET) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jan 2019 06:14:42 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,503,1539673200"; d="scan'208";a="313551202" Received: from aburakov-mobl1.ger.corp.intel.com (HELO [10.237.220.84]) ([10.237.220.84]) by fmsmga005.fm.intel.com with ESMTP; 21 Jan 2019 06:14:41 -0800 To: "Eads, Gage" , "Richardson, Bruce" Cc: "dev@dpdk.org" , "olivier.matz@6wind.com" , "arybchenko@solarflare.com" , "Ananyev, Konstantin" References: <20190110210122.24889-1-gage.eads@intel.com> <20190110210122.24889-2-gage.eads@intel.com> <20190111105848.GA18132@bricha3-MOBL.ger.corp.intel.com> <9b215f62-55e3-5ffd-d163-0a8c9e7fa55a@intel.com> <20190111115851.GC3336@bricha3-MOBL.ger.corp.intel.com> <9184057F7FC11744A2107296B6B8EB1E541C4C91@FMSMSX108.amr.corp.intel.com> From: "Burakov, Anatoly" Message-ID: Date: Mon, 21 Jan 2019 14:14:40 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <9184057F7FC11744A2107296B6B8EB1E541C4C91@FMSMSX108.amr.corp.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [PATCH 1/6] ring: change head and tail to pointer-width size 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: Mon, 21 Jan 2019 14:14:44 -0000 On 11-Jan-19 7:27 PM, Eads, Gage wrote: > > >> -----Original Message----- >> From: Richardson, Bruce >> Sent: Friday, January 11, 2019 5:59 AM >> To: Burakov, Anatoly >> Cc: Eads, Gage ; dev@dpdk.org; >> olivier.matz@6wind.com; arybchenko@solarflare.com; Ananyev, Konstantin >> >> Subject: Re: [dpdk-dev] [PATCH 1/6] ring: change head and tail to pointer-width >> size >> >> On Fri, Jan 11, 2019 at 11:30:24AM +0000, Burakov, Anatoly wrote: >>> On 11-Jan-19 10:58 AM, Bruce Richardson wrote: >>>> On Fri, Jan 11, 2019 at 10:40:19AM +0000, Burakov, Anatoly wrote: >>>>> <...> >>>>> >>>>>> + * Copyright(c) 2016-2019 Intel Corporation >>>>>> */ >>>>>> /** >>>>>> @@ -88,7 +88,7 @@ rte_event_ring_enqueue_burst(struct >> rte_event_ring *r, >>>>>> const struct rte_event *events, >>>>>> unsigned int n, uint16_t *free_space) >>>>>> { >>>>>> - uint32_t prod_head, prod_next; >>>>>> + uintptr_t prod_head, prod_next; >>>>> >>>>> I would also question the use of uinptr_t. I think semnatically, >>>>> size_t is more appropriate. >>>>> >>>> Yes, it would, but I believe in this case they want to use the >>>> largest size of (unsigned)int where there exists an atomic for >>>> manipulating 2 of them simultaneously. [The largest size is to >>>> minimize any chance of an ABA issue occuring]. Therefore we need >>>> 32-bit values on 32-bit and 64-bit on 64, and I suspect the best way >>>> to guarantee this is to use pointer-sized values. If size_t is >>>> guaranteed across all OS's to have the same size as uintptr_t it could also be >> used, though. >>>> >>>> /Bruce >>>> >>> >>> Technically, size_t and uintptr_t are not guaranteed to match. In >>> practice, they won't match only on architectures that DPDK doesn't >>> intend to run on (such as 16-bit segmented archs, where size_t would >>> be 16-bit but uinptr_t would be 32-bit). >>> >>> In all the rest of DPDK code, we use size_t for this kind of thing. >>> >> >> Ok. >> If we do use size_t, I think we also need to add a compile-time check into the >> build too, to error out if sizeof(size_t) != sizeof(uintptr_t). > > Ok, I wasn't aware of the precedent of using size_t for this purpose. I'll change it and look into adding a static assert. RTE_BUILD_BUG_ON? > > Thanks, > Gage > -- Thanks, Anatoly