From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 97748C433EF for ; Wed, 19 Jan 2022 11:53:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=cSnPRIc6ephJgc88+qEb+gnOuwGrFeuUhgmmjXrRp4o=; b=Js1Bncc+x+UD1S 5O8QYCmH5pdZFdN3jX/jqE1RVn5tBW68gXzmaAEZXMAXz6e1y3YqHEUm8ceYY6iWoneQYSoYfwggb vbkB2fR8UyCxmCoW/y7F6TvEOtU4RoRCMWT0RCX8NwwLBTnvz8CqMc4e4Ut/lMHwR3B+ruxPo/q7D pOeWL3a5W8eMciW/M5UEUWD6Uy/CQRvtswzc5+K17zJEhdsvx5cuVVH4gGMN6FK1cQLIDqecVZBRg Xh5HLjUUIbex9q1x6i2B75egf7KyxsJQw+mARIkE5QaV/XXGuw1fVLkBVdt/75nF2ffo8sqU6ujIi 8208D10xDegJtw4i3vwg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nA9Vs-005FsW-KC; Wed, 19 Jan 2022 11:52:28 +0000 Received: from ams.source.kernel.org ([145.40.68.75]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nA9Vl-005FpK-U2; Wed, 19 Jan 2022 11:52:24 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 92085B8199C; Wed, 19 Jan 2022 11:52:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2160C004E1; Wed, 19 Jan 2022 11:52:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1642593139; bh=QfpuL80/duahPHOR1KalTLy06DYEW34Je3XdZ5Xf75o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=m20X0mJ3MzAXLJNXcmWwhF/O7iTUjdtfIexfjhZORLToSTg97fm/4gM9W6iaJgCeK LDE/VvkdorLX7OPmUYCHGd3iKRDjEBlEAY51Mjrnj75VWOSjRPbgHbDK099v510ybO i68wLNd1mS+hqMXQIKZyTtGLrBtmVYVgrOougnyK5KWeXCiM1YqF7+rfOyxiID29p+ KyGnJZFjKCTbNwPDlmuHFFOzU3MSLGpfF1Kjf1CKGFiSDMafyPeyHobNAcCXSTWE6r Sykn4NY72ExihyXhecuVSwaJbwbTciTKlU2coZTaPjAn9IUSdFe7ru4In6WdKyec3k WRmakSOBFkXcA== Date: Wed, 19 Jan 2022 19:44:35 +0800 From: Jisheng Zhang To: Baoquan He Cc: Alexandre Ghiti , Russell King , Catalin Marinas , Will Deacon , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, hpa@zytor.com, Eric Biederman , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, kexec@lists.infradead.org, Alexandre ghiti Subject: Re: [PATCH v2 0/5] kexec: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef Message-ID: References: <20211206160514.2000-1-jszhang@kernel.org> <20220116133847.GE2388@MiWiFi-R3L-srv> <20220119080859.GB4977@MiWiFi-R3L-srv> <20220119093322.GC4977@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220119093322.GC4977@MiWiFi-R3L-srv> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220119_035222_281529_FF3FD9A0 X-CRM114-Status: GOOD ( 34.24 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jan 19, 2022 at 05:33:22PM +0800, Baoquan He wrote: > On 01/19/22 at 09:52am, Alexandre Ghiti wrote: > > Hi Baoquan, > > > > On Wed, Jan 19, 2022 at 9:11 AM Baoquan He wrote: > > > > > > On 01/18/22 at 10:13pm, Jisheng Zhang wrote: > > > > On Sun, Jan 16, 2022 at 09:38:47PM +0800, Baoquan He wrote: > > > > > Hi Jisheng, > > > > > > > > Hi Baoquan, > > > > > > > > > > > > > > On 12/07/21 at 12:05am, Jisheng Zhang wrote: > > > > > > Replace the conditional compilation using "#ifdef CONFIG_KEXEC_CORE" > > > > > > by a check for "IS_ENABLED(CONFIG_KEXEC_CORE)", to simplify the code > > > > > > and increase compile coverage. > > > > > > > > > > I go through this patchset, You mention the benefits it brings are > > > > > 1) simplity the code; > > > > > 2) increase compile coverage; > > > > > > > > > > For benefit 1), it mainly removes the dummy function in x86, arm and > > > > > arm64, right? > > > > > > > > Another benefit: remove those #ifdef #else #endif usage. Recently, I > > > > fixed a bug due to lots of "#ifdefs": > > > > http://lists.infradead.org/pipermail/linux-riscv/2021-December/010607.html > > > > > > Glad to know the fix. While, sometime the ifdeffery is necessary. I am > > > sorry about the one in riscv and you have fixed, it's truly a bug . But, > > > the increasing compile coverage at below you tried to make, it may cause > > > issue. Please see below my comment. > > > > > > > > > > > > > > > > > For benefit 2), increasing compile coverage, could you tell more how it > > > > > achieves and why it matters? What if people disables CONFIG_KEXEC_CORE in > > > > > purpose? Please forgive my poor compiling knowledge. > > > > > > > > Just my humble opinion, let's compare the code:: > > > > > > > > #ifdef CONFIG_KEXEC_CORE > > > > > > > > code block A; > > > > > > > > #endif > > > > > > > > If KEXEC_CORE is disabled, code block A won't be compiled at all, the > > > > preprocessor will remove code block A; > > > > > > > > If we convert the code to: > > > > > > > > if (IS_ENABLED(CONFIG_KEXEC_CORE)) { > > > > code block A; > > > > } > > > > > > > > Even if KEXEC_CORE is disabled, code block A is still compiled. > > > > > > This is what I am worried about. Before, if CONFIG_KEXEC_CORE is > > > unset, those relevant codes are not compiled in. I can't see what > > > benefit is brought in if compiled in the unneeded code block. Do I miss > > > anything? > > > > > > > This is explained in Documentation/process/coding-style.rst "21) > > Conditional Compilation". > > Thanks for the pointer, Alex. > > I read that part, while my confusion isn't gone. With the current code, > CONFIG_KEXEC_CORE is set, > - reserve_crashkernel_low() and reserve_crashkernel() compiled in. Although the code block will be compiled, but the code block will be optimized out. > CONFIG_KEXEC_CORE is unset, > - reserve_crashkernel_low() and reserve_crashkernel() compiled out. > > After this patch applied, does it have the same effect as the old code? I compared the .o, and can confirm they acchieve the same effect. > > arch/x86/kernel/setup.c: > > before > ====== > #ifdef CONFIG_KEXEC_CORE > static int __init reserve_crashkernel_low(void) > { > ...... > } > static void __init reserve_crashkernel(void) > { > ...... > } > #else > static void __init reserve_crashkernel(void) > { > } > #endif > > after > ======= > static int __init reserve_crashkernel_low(void) > { > ...... > } > static void __init reserve_crashkernel(void) > { > ...... > if (!IS_ENABLED(CONFIG_KEXEC_CORE)) > return; > ...... > } > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel