From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Burakov, Anatoly" Subject: Re: [PATCH 1/6] ring: change head and tail to pointer-width size Date: Mon, 21 Jan 2019 14:14:40 +0000 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" , "olivier.matz@6wind.com" , "arybchenko@solarflare.com" , "Ananyev, Konstantin" To: "Eads, Gage" , "Richardson, Bruce" 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) In-Reply-To: <9184057F7FC11744A2107296B6B8EB1E541C4C91@FMSMSX108.amr.corp.intel.com> Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 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