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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 79424C169C4 for ; Mon, 11 Feb 2019 10:57:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 46D4C20838 for ; Mon, 11 Feb 2019 10:57:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="0U7b+TSC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727063AbfBKK5y (ORCPT ); Mon, 11 Feb 2019 05:57:54 -0500 Received: from merlin.infradead.org ([205.233.59.134]:39280 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726045AbfBKK5x (ORCPT ); Mon, 11 Feb 2019 05:57:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=H4FKzYfPZLq064fpvMaxRyPbo6mwWdcW0fXgF0VWycY=; b=0U7b+TSCrog3RuwY+5aIN+sYF hv/X24vYbiLjaTad2ObIWMdW7Cp2r/5OoaUpAoXctxc/VYvLlvd8Jg876MzN8pgTjMW8CZ3P1r/K0 V/l2fLFDfV1pgkRUFU9xzkmvMbliuyWhgYyM+5CQxhzMD875i3oOU3bLFnwzd6Z1n69EGanR7kB8K jwNrR1x25pUNYuM1WWMfiO/CFWtHodA2Mmztx2gmUubEivvDlwHAS5qsyCdKdk3uPgvtfWI5OmsKO 4D+eGwN6yN1S/MmNn/tvUdF/HvrjMc60lzn96bluUcUP+BS/cOvXQ1En41wBhdBg2BY4eZU6c4md3 EkSdmP65w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gt9HI-0007Ng-0y; Mon, 11 Feb 2019 10:57:32 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 535FA20D0E3CF; Mon, 11 Feb 2019 11:57:29 +0100 (CET) Date: Mon, 11 Feb 2019 11:57:29 +0100 From: Peter Zijlstra To: Waiman Long Cc: Ingo Molnar , Will Deacon , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, x86@kernel.org, Arnd Bergmann , Borislav Petkov , "H. Peter Anvin" , Davidlohr Bueso , Linus Torvalds , Andrew Morton , Tim Chen Subject: Re: [PATCH] locking/rwsem: Remove arch specific rwsem files Message-ID: <20190211105729.GH32534@hirez.programming.kicks-ass.net> References: <1549850450-10171-1-git-send-email-longman@redhat.com> <20190211093601.GT32511@hirez.programming.kicks-ass.net> <20190211094044.GG32534@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190211094044.GG32534@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 11, 2019 at 10:40:44AM +0100, Peter Zijlstra wrote: > On Mon, Feb 11, 2019 at 10:36:01AM +0100, Peter Zijlstra wrote: > > On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote: > > > +static inline int __down_read_trylock(struct rw_semaphore *sem) > > > +{ > > > + long tmp; > > > + > > > + while ((tmp = atomic_long_read(&sem->count)) >= 0) { > > > + if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, > > > + tmp + RWSEM_ACTIVE_READ_BIAS)) { > > > + return 1; > > > > That really wants to be: > > > > if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, > > tmp + RWSEM_ACTIVE_READ_BIAS)) > > > > > + } > > > + } > > > + return 0; > > > +} > > Also, the is the one case where LL/SC can actually do 'better'. Do you > have benchmarks for say PowerPC or ARM64 ? Ah, I see they already used asm-generic/rwsem.h which has similar code to the above.