From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ferruh Yigit Subject: Re: [PATCH 0/5] remove usage of register keyword in C Date: Thu, 23 Aug 2018 14:07:18 +0100 Message-ID: References: <20180731163059.27085-1-stephen@networkplumber.org> <20180731164840.GD5211@6wind.com> <20180731110737.38555f02@xeon-e3> <50204CDA-B4AD-44C8-AB07-2FE9C2A412C0@mellanox.com> <20180801140356.5ac88c43@xeon-e3> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Adrien Mazarguil , "dev@dpdk.org" To: Stephen Hemminger , Yongseok Koh Return-path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by dpdk.org (Postfix) with ESMTP id 497572C4F for ; Thu, 23 Aug 2018 15:07:24 +0200 (CEST) In-Reply-To: <20180801140356.5ac88c43@xeon-e3> 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 8/1/2018 10:03 PM, Stephen Hemminger wrote: > On Wed, 1 Aug 2018 18:03:04 +0000 > Yongseok Koh wrote: > >>> On Jul 31, 2018, at 11:07 AM, Stephen Hemminger wrote: >>> >>> On Tue, 31 Jul 2018 18:48:40 +0200 >>> Adrien Mazarguil wrote: >>> >>>> On Tue, Jul 31, 2018 at 09:30:54AM -0700, Stephen Hemminger wrote: >>>>> Declaring variables as register in C is a leftover from an earlier >>>>> era (like cassette tape decks in cars). >>>> >>>> I don't agree here. It's a hint for compilers and developers that the >>>> address of such variables won't be needed (and cannot be taken) to enable >>>> whatever optimizations are possible knowing this. >>>> >>>> Somewhat like inline functions, it's not a forced optimization, just a >>>> useful hint that shouldn't hurt if used wisely. >>>> >>>> Besides, cassette decks are not dead yet :) >>> >>> If you look at the code, that is not how register is being used (ie. don't take >>> address of this). It seems like an attempt at optimization. >> >> I know compilers are smart enough and the occurrences in mlx4/5 were made from >> my old fashioned habit. But, I don't see any urgency to push this patch in RC >> stage even though I'm 99% sure that it is harmless. And in general I don't even >> understand why we can't live with that if it isn't harmful (or a violation) but >> informative. I mean no badness but at least one goodness :-) >> >> Thanks, >> Yongseok >> > > Sure, this is intended for next release not rc stage. > Just trying to clean up code base where I see it. I agree with Yongseok, at worst they show the intention of the developer, I don't see motivation to remove them unless they are doing something wrong, which seems not the reason of this patch. And although I found some information that says "register" ignored completely for gcc, I can see it differs when optimization disabled. I am not saying practically it differs, since we enable optimization expect from debugging, most probably there is no practical difference between having the keyword or not, but what I am trying to say is it not completely ignored either.