From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH 11/12] sched: use for_each_if in topology.h Date: Mon, 9 Jul 2018 17:52:04 +0200 Message-ID: <20180709155204.GD3008@phenom.ffwll.local> References: <20180709083650.23549-1-daniel.vetter@ffwll.ch> <20180709083650.23549-11-daniel.vetter@ffwll.ch> <20180709103656.GH2476@hirez.programming.kicks-ass.net> <20180709151258.GV2476@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <20180709151258.GV2476@hirez.programming.kicks-ass.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: Peter Zijlstra Cc: Daniel Vetter , Intel Graphics Development , LKML , DRI Development , Daniel Vetter , Andrew Morton List-Id: dri-devel@lists.freedesktop.org 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header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933729AbeGIPwL (ORCPT ); Mon, 9 Jul 2018 11:52:11 -0400 Received: from mail-ed1-f67.google.com ([209.85.208.67]:45521 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933374AbeGIPwI (ORCPT ); Mon, 9 Jul 2018 11:52:08 -0400 Received: by mail-ed1-f67.google.com with SMTP id i20-v6so1296806eds.12 for ; Mon, 09 Jul 2018 08:52:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=sender:date:from:to:cc:subject:message-id:mail-followup-to :references:mime-version:content-disposition:in-reply-to:user-agent; bh=3k83YPOjMQc9TxIjIfULVIR2/Ixa1HISJxm3xzghrfM=; b=jpSnKR6li/TUFqvkmBmpAwJWgsWc5EEPqjfExK7xowJ3bLuV2qyjfilcw1Ttqoturi u8R3uWamZCixl9RvMMS1QxEQRQKbUMwTDU46G9YIxerw8zdPFS02Sc5YuICY2fdvnV7u 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-0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:5628:0:496f:7dc5:66d7:a057]) by smtp.gmail.com with ESMTPSA id u3-v6sm972949edo.44.2018.07.09.08.52.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 09 Jul 2018 08:52:06 -0700 (PDT) Date: Mon, 9 Jul 2018 17:52:04 +0200 From: Daniel Vetter To: Peter Zijlstra Cc: Daniel Vetter , LKML , DRI Development , Intel Graphics Development , Daniel Vetter , Andrew Morton Subject: Re: [PATCH 11/12] sched: use for_each_if in topology.h Message-ID: <20180709155204.GD3008@phenom.ffwll.local> Mail-Followup-To: Peter Zijlstra , LKML , DRI Development , Intel Graphics Development , Daniel Vetter , Andrew Morton References: <20180709083650.23549-1-daniel.vetter@ffwll.ch> <20180709083650.23549-11-daniel.vetter@ffwll.ch> <20180709103656.GH2476@hirez.programming.kicks-ass.net> <20180709151258.GV2476@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180709151258.GV2476@hirez.programming.kicks-ass.net> X-Operating-System: Linux phenom 4.14.0-3-amd64 User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 09, 2018 at 05:12:58PM +0200, Peter Zijlstra wrote: > On Mon, Jul 09, 2018 at 05:00:07PM +0200, Daniel Vetter wrote: > > On Mon, Jul 9, 2018 at 12:36 PM, Peter Zijlstra wrote: > > > On Mon, Jul 09, 2018 at 10:36:49AM +0200, Daniel Vetter wrote: > > > >> #define for_each_node_with_cpus(node) \ > > >> for_each_online_node(node) \ > > >> - if (nr_cpus_node(node)) > > >> + for_each_if (nr_cpus_node(node)) > > > > > > Not having gotten any of the other patches, I'm not really sure what > > > this does and such, but improve readability it does not :/ > > > > Patch 1 in this series, which I dumped onto lkml as a whole: > > > > https://lkml.org/lkml/2018/7/9/179 > > Right, so while I don't object to being Cc'ed to the whole series, I do > mind not being Cc'ed to at least the generic bits required to understand > the patch I do have to look at. > > > Imo it does improve readability for the if (!cond) {} else pattern. > > And (assuming my grep fu isn't too badly wrong) most places in the > > kernel do use this pattern in for_each macros, so I guess its a real > > thing. We've definitely hit it plenty in drm iterators (but we seem to > > like if() checks in iterator macros maybe a bit too much). > > > > I'm happy to drop this patch tough if you deem it offensive. > > I'd just like to understand it better; what compiler complains about > this and is the warning otherwise useful? These things don't seem > mentioned in that initial patch either. > > IOW I suppose I'm asking for the justification of this churn. If it's > really needed and useful so be it, but so far I'm not seeing any. > > At a while guess I'd say this is something new in gcc-8 (and while I > have that installed on some machines, it doesn't seem to be the default, > and so I've not actually seen its output). But is the warning actually > useful, should we not just kill the warning like we tend to do some > really silly ones. for_each_something(foo) if (foo->bla) call_bla(foo); else call_default(foo); Totally contrived, but this complains. Liberally sprinkling {} also shuts up the compiler, but it's a bit confusing given that a plain for {;;} is totally fine. And it's confusing since at first glance the compiler complaining about nested if and ambigous else doesn't make sense since clearly there's only 1 if there. Wrt this being useful or not: We've had it for a while in drm, and Andy and Yishen where rolling yet another open coded version of this on a patch that flew past me on dri-devel. So I pointed them at the for_each_if() we have and typed this series to move it to kernel.h. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch