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 X-Spam-Level: X-Spam-Status: No, score=-14.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88E0AC433EF for ; Tue, 14 Sep 2021 13:56:08 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4F7356113B for ; Tue, 14 Sep 2021 13:56:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 4F7356113B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org 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=L/W7ncXCAxrPcZTTKA7UDvgnXHdaP3kMgU2S9pKCeuU=; b=E6/noraMF44oJh HyFPJPBi4kIo2DCwiWtsBpuXmKIFE+MF2qL6ZQGoztKEmyr5WPJ+Gntk+N08Flte5JgnzTZ73IJl+ sKmFCWYvPXX5/KjL1A+sHuuPcMqWlzRmfSAStsjBmwRxqBDpkJKFBz6c7JKOCbtn84MnbBJDoeqma XMkeE51X3zlrjZXwDN+tvOtD0l1qINwWOPGrSSUwwqc+7Mk+zIMmT2wODSM0YU6xjwM1JFUJYVQma FjG8FOW3ArFszbTGPVu8rqygErED9PLTkuFEX9Lr80oMMkvBkVyy3tl9a05sZKHP6+fFxM+HEb/RL Qver2yhya29iSZfYINsA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQ8un-005v0U-3c; Tue, 14 Sep 2021 13:56:01 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQ8uO-005uqz-La; Tue, 14 Sep 2021 13:55:38 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9D62A1FB; Tue, 14 Sep 2021 06:55:33 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.21.233]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8D39B3F5A1; Tue, 14 Sep 2021 06:55:29 -0700 (PDT) Date: Tue, 14 Sep 2021 14:55:27 +0100 From: Mark Rutland To: Ard Biesheuvel Cc: linux-kernel@vger.kernel.org, Keith Packard , Russell King , Catalin Marinas , Will Deacon , Michael Ellerman , Benjamin Herrenschmidt , Christophe Leroy , Paul Mackerras , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Kees Cook , Andy Lutomirski , Linus Torvalds , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org Subject: Re: [RFC PATCH 0/8] Move task_struct::cpu back into thread_info Message-ID: <20210914135527.GC30247@C02TD0UTHF1T.local> References: <20210914121036.3975026-1-ardb@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210914121036.3975026-1-ardb@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210914_065536_894014_CEFE76B0 X-CRM114-Status: GOOD ( 26.83 ) X-BeenThere: linux-riscv@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-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, Sep 14, 2021 at 02:10:28PM +0200, Ard Biesheuvel wrote: > Commit c65eacbe290b ("sched/core: Allow putting thread_info into > task_struct") mentions that, along with moving thread_info into > task_struct, the cpu field is moved out of the former into the latter, > but does not explain why. >From what I recall of talking to Andy around that time, when converting arm64 over, the theory was that over time we'd move more and more out of thread_info and into task_struct or thread_struct, until task_struct supplanted thread_info entirely, and that all became generic. I think the key gain there was making things more *generic*, and there are other ways we could do that in future without moving more into task_struct (e.g. with a geenric thread_info and arch_thread_info inside that). With that in mind, and given the diffstat, I think this is worthwhile. FWIW, for the series: Acked-by: Mark Rutland Mark. > While collaborating with Keith on adding THREAD_INFO_IN_TASK support to > ARM, we noticed that keeping CPU in task_struct is problematic for > architectures that define raw_smp_processor_id() in terms of this field, > as it requires linux/sched.h to be included, which causes a lot of pain > in terms of circular dependencies (or 'header soup', as the original > commit refers to it). > > For examples of how existing architectures work around this, please > refer to patches #6 or #7. In the former case, it uses an awful > asm-offsets hack to index thread_info/current without using its type > definition. The latter approach simply keeps a copy of the task_struct > CPU field in thread_info, and keeps it in sync at context switch time. > > Patch #8 reverts this latter approach for ARM, but this code is still > under review so it does not currently apply to mainline. > > We also discussed introducing yet another Kconfig symbol to indicate > that the arch has THREAD_INFO_IN_TASK enabled but still prefers to keep > its CPU field in thread_info, but simply keeping it in thread_info in > all cases seems to be the cleanest approach here. > > Cc: Keith Packard > Cc: Russell King > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Michael Ellerman > Cc: Benjamin Herrenschmidt > Cc: Christophe Leroy > Cc: Paul Mackerras > Cc: Paul Walmsley > Cc: Palmer Dabbelt > Cc: Albert Ou > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Christian Borntraeger > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: Peter Zijlstra > Cc: Kees Cook > Cc: Andy Lutomirski > Cc: Linus Torvalds > Cc: Arnd Bergmann > Cc: linux-arm-kernel@lists.infradead.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: linux-riscv@lists.infradead.org > Cc: linux-s390@vger.kernel.org > > Ard Biesheuvel (8): > arm64: add CPU field to struct thread_info > x86: add CPU field to struct thread_info > s390: add CPU field to struct thread_info > powerpc: add CPU field to struct thread_info > sched: move CPU field back into thread_info if THREAD_INFO_IN_TASK=y > powerpc: smp: remove hack to obtain offset of task_struct::cpu > riscv: rely on core code to keep thread_info::cpu updated > ARM: rely on core code to keep thread_info::cpu updated > > arch/arm/include/asm/switch_to.h | 14 -------------- > arch/arm/kernel/smp.c | 3 --- > arch/arm64/include/asm/thread_info.h | 1 + > arch/arm64/kernel/asm-offsets.c | 2 +- > arch/arm64/kernel/head.S | 2 +- > arch/powerpc/Makefile | 11 ----------- > arch/powerpc/include/asm/smp.h | 17 +---------------- > arch/powerpc/include/asm/thread_info.h | 3 +++ > arch/powerpc/kernel/asm-offsets.c | 4 +--- > arch/powerpc/kernel/smp.c | 2 +- > arch/riscv/kernel/asm-offsets.c | 1 - > arch/riscv/kernel/entry.S | 5 ----- > arch/riscv/kernel/head.S | 1 - > arch/s390/include/asm/thread_info.h | 1 + > arch/x86/include/asm/thread_info.h | 3 +++ > include/linux/sched.h | 6 +----- > kernel/sched/sched.h | 4 ---- > 17 files changed, 14 insertions(+), 66 deletions(-) > > -- > 2.30.2 > _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv