From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 857FF13AA2F; Thu, 24 Oct 2024 13:01:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729774922; cv=none; b=Fa0C/dXQAcwW1ivepoKVk0y2/bV6QwMK8j4FW0bmPSRJ6fzXzpnQEhy3FtuA5jE1M+kV/OFf13Ran/ptBvrMLC02ounR0RYUxuh7hEtfjidwhWyITsz6RcuAZK6VNEPH2f3xAW7DZLCSsVIgDN6zKGGdBO68URluZD3R3hxlX9k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729774922; c=relaxed/simple; bh=2a+9bKMv7hVzknlW8OazkLUPwrbxo5rblBY4AWBW2pI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=K85ZJaSxdDR/IKkWELAHAUfv243vE4M/GGc5M/ErSX6XqrZW0lEUkre0CM0Rm1AudFrw4MxtLHZueG56fG6Q02gWvDsnjeTe3wVdadpIj0ESilf86b5szTfdAJcnTWcXdiNm3+WD8ylT8fK3fxs14n3+Qv6HWv68TWAMZi0RmD4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=CY16NWev; arc=none smtp.client-ip=192.198.163.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="CY16NWev" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1729774920; x=1761310920; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=2a+9bKMv7hVzknlW8OazkLUPwrbxo5rblBY4AWBW2pI=; b=CY16NWevZLqXhEQXvK2bSE8cctLfnDvkuCnioOYL1v5/fD3YDiqwtqav aau4N+yyKYP3cin+80GOghhIUEsC5f2jp5wAwWkg7jfzQkqPLb6d58gXV ZJLA+FKaeTBWWE/m/XcPV2zmW1GN+xVsh9+FQuwgMcaUV6Fkk6G1RIwY5 9g9uqsl/WzWJsoMSo+2urQpUwRSksW3XNcfPFFXrbOYoGhoJ2LU5yFLhc Ec/StMBCCyhDidJJNTfvSzsduWDf1URsGgpJ44D5AQV11RN4toTRBh0z/ MC+mcoSZZ7fyQM0uHiTiuoRXRhvHp50K2LcILnj+aoMrQMx8xZ8G6kosC Q==; X-CSE-ConnectionGUID: o0GGTXs5S4qLRfRStS2F0g== X-CSE-MsgGUID: GSNgBoBPSRSjhG+Oz0Udcw== X-IronPort-AV: E=McAfee;i="6700,10204,11235"; a="29303306" X-IronPort-AV: E=Sophos;i="6.11,229,1725346800"; d="scan'208";a="29303306" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Oct 2024 06:01:59 -0700 X-CSE-ConnectionGUID: Cd4N0AKgRuanQXpDlER8KQ== X-CSE-MsgGUID: BgcMOECEQKqvDTOvgmvjfQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.11,229,1725346800"; d="scan'208";a="85191643" Received: from smile.fi.intel.com ([10.237.72.154]) by fmviesa004.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Oct 2024 06:01:56 -0700 Received: from andy by smile.fi.intel.com with local (Exim 4.98) (envelope-from ) id 1t3xTM-00000006Zui-3IcU; Thu, 24 Oct 2024 16:01:52 +0300 Date: Thu, 24 Oct 2024 16:01:52 +0300 From: Andy Shevchenko To: "Huang, Ying" Cc: Dan Williams , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, Davidlohr Bueso , Jonathan Cameron , Alistair Popple , Bjorn Helgaas , Baoquan He , Dave Jiang , Alison Schofield Subject: Re: [RFC] resource: Avoid unnecessary resource tree walking in __region_intersects() Message-ID: References: <20241010065558.1347018-1-ying.huang@intel.com> <87set3a1nm.fsf@yhuang6-desk2.ccr.corp.intel.com> <671965a8b37a2_1bbc629489@dwillia2-xfh.jf.intel.com.notmuch> <87wmhx3cpc.fsf@yhuang6-desk2.ccr.corp.intel.com> Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wmhx3cpc.fsf@yhuang6-desk2.ccr.corp.intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo On Thu, Oct 24, 2024 at 08:30:39PM +0800, Huang, Ying wrote: > Andy Shevchenko writes: > > On Wed, Oct 23, 2024 at 02:07:52PM -0700, Dan Williams wrote: > >> Andy Shevchenko wrote: > >> > On Fri, Oct 11, 2024 at 09:06:37AM +0800, Huang, Ying wrote: > >> > > David Hildenbrand writes: > >> > > > On 10.10.24 08:55, Huang Ying wrote: ... > >> > > > for ((_p) = (_root)->child; (_p); (_p) = next_resource_XXX(_root, _p)) > >> > > > >> > > Yes. This can improve code readability. > >> > > > >> > > A possible issue is that "_root" will be evaluated twice in above macro > >> > > definition. IMO, this should be avoided. > >> > > >> > Ideally, yes. But how many for_each type of macros you see that really try hard > >> > to achieve that? I believe we shouldn't worry right now about this and rely on > >> > the fact that root is the given variable. Or do you have an example of what you > >> > suggested in the other reply, i.e. where it's an evaluation of the heavy call? > >> > > >> > > Do you have some idea about > >> > > how to do that? Something like below? > >> > > > >> > > #define for_each_resource_XXX(_root, _p) \ > >> > > for (typeof(_root) __root = (_root), __p = (_p) = (__root)->child; \ > >> > > __p && (_p); (_p) = next_resource_XXX(__root, _p)) > >> > > >> > This is a bit ugly :-( I would avoid ugliness as long as we have no problem to > >> > solve (see above). > >> > >> Using a local defined variable to avoid double evaluation is standard > >> practice. I do not understand "avoid ugliness as long as we have no problem to > >> solve", the problem to solve will be if someone accidentally does > >> something like "for_each_resource_descendant(root++, res)". *That* will > >> be a problem when someone finally realizes that the macro is hiding a > >> double evaluation. > > > > Can you explain, why do we need __p and how can we get rid of that? > > I understand the part of the local variable for root. > > If don't use '__p', the macro becomes > > #define for_each_resource_XXX(_root, _p) \ > for (typeof(_root) __root = (_root), (_p) = (__root)->child; \ > (_p); (_p) = next_resource_XXX(__root, _p)) > > Where, '_p' must be a variable name, and it will be a new variable > inside for loop and mask the variable with same name outside of macro. > IIUC, this breaks the macro convention in kernel and has subtle variable > masking semantics. Yep. In property.h nobody cares about evaluation which makes the macro as simple as #define for_each_resource_XXX(_root, _p) \ for (_p = next_resource_XXX(__root, NULL); _p; \ _p = next_resource_XXX(__root, _p)) (Dan, that's what I called to avoid solving issues we don't have and most likely will never have.) but if you want to stick with your variant some improvements can be done: #define for_each_resource_XXX(_root, _p) \ for (typeof(_root) __root = (_root), __p = _p = __root->child; \ __p && _p; _p = next_resource_XXX(__root, _p)) 1) no need to have local variable in parentheses; 2) no need to have iterator in parentheses, otherwise it would be crazy code that has put something really wrong there and still expect the thing to work. > >> So no, this proposal is not "ugly", it is a best practice. See the > >> definition of min_not_zero() for example. > > > > I know that there are a lot of macros that look uglier that this one. -- With Best Regards, Andy Shevchenko