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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 16D2CC43381 for ; Fri, 22 Mar 2019 19:33:42 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 8FC6D20870 for ; Fri, 22 Mar 2019 19:33:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FC6D20870 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=stgolabs.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 44Qv366JnmzDqS0 for ; Sat, 23 Mar 2019 06:33:38 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=softfail (mailfrom) smtp.mailfrom=stgolabs.net (client-ip=195.135.220.15; helo=mx1.suse.de; envelope-from=dave@stgolabs.net; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=stgolabs.net Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 44QtzZ3KxgzDqRq for ; Sat, 23 Mar 2019 06:30:27 +1100 (AEDT) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id B825BAFCF; Fri, 22 Mar 2019 19:30:22 +0000 (UTC) Date: Fri, 22 Mar 2019 12:30:10 -0700 From: Davidlohr Bueso To: Linus Torvalds Subject: Re: [PATCH v5 1/3] locking/rwsem: Remove arch specific rwsem files Message-ID: <20190322193010.azb7rmmmaclhal35@linux-r8p5> References: <20190322143008.21313-1-longman@redhat.com> <20190322143008.21313-2-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180323 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, Linux-sh list , Peter Zijlstra , Will Deacon , linux-mips@vger.kernel.org, "H. Peter Anvin" , sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arch , linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, linux-hexagon@vger.kernel.org, the arch/x86 maintainers , Ingo Molnar , Waiman Long , uclinux-h8-devel@lists.sourceforge.jp, linux-xtensa@linux-xtensa.org, Arnd Bergmann , linux-um@lists.infradead.org, linux-m68k , openrisc@lists.librecores.org, Borislav Petkov , Thomas Gleixner , "linux-alpha@vger.kernel.org" , linux-parisc@vger.kernel.org, Tim Chen , Linux List Kernel Mailing , "linux-alpha@vger.kernel.org" , nios2-dev@lists.rocketboards.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, 22 Mar 2019, Linus Torvalds wrote: >Some of them _might_ be performance-critical. There's the one on >mmap_sem in the fault handling path, for example. And yes, I'd expect >the normal case to very much be "no other readers or writers" for that >one. Yeah, the mmap_sem case in the fault path is really expecting an unlocked state. To the point that four archs have added branch predictions, ie: 92181f190b6 (x86: optimise x86's do_page_fault (C entry point for the page fault path)) b15021d994f (powerpc/mm: Add a bunch of (un)likely annotations to do_page_fault) And using PROFILE_ANNOTATED_BRANCHES shows pretty clearly: (without resetting the counters) correct incorrect % Function File Line ------- --------- - -------- ---- ---- 4603685 34 0 do_user_addr_fault fault.c 1416 (bootup) 382327745 449 0 do_user_addr_fault fault.c 1416 (kernel build) 399446159 461 0 do_user_addr_fault fault.c 1416 (redis benchmark) It would probably wouldn't harm doing the unlikely() for all archs, or alternatively, add likely() to the atomic_long_try_cmpxchg_acquire in patch 3 and do it implicitly but maybe that would be less flexible(?) Thanks, Davidlohr