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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 425A3C6778A for ; Thu, 5 Jul 2018 17:59:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E608023DB7 for ; Thu, 5 Jul 2018 17:59:14 +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="udRPyPsu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E608023DB7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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 S1753854AbeGER7L (ORCPT ); Thu, 5 Jul 2018 13:59:11 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:36166 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753661AbeGER7J (ORCPT ); Thu, 5 Jul 2018 13:59:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=/MwNrZ5TZX+cnUrZUFCwVIDza/pl1zHKiftiVe5yN3U=; b=udRPyPsuujLlkR5kjj3ZYnPZW 6WrYuoSpU9BQTHNISsrJHHlPIGJJp4qq/ez33RPGZen/hRjzaeoHWUuh/pdtIjkIW2eAMBu5mxA4e oOMqf4cGXhP4GroHsV+wRVA7lR4hOoQwtAQngwOrqzXEex4P+8rZ8214kG5pOpdExgrzPXc84x1dN yoYK806frDt25FEB/zxWrSOEum7TMOVp7J+uWYXxAGMsT721XwyUmvwcrLi8mEOlNqXr10MAAfdeq RHOIL83z/AvITP1LJuYodaYpOv9T/wiCAuj6iDEZT07gMrCwYr/6ra0Qyjuij+AZq8RlYwNygp/mz RnJ2G+s3g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fb8X1-0001ex-V7; Thu, 05 Jul 2018 17:59:04 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 4C2CE20289CF4; Thu, 5 Jul 2018 19:59:02 +0200 (CEST) Date: Thu, 5 Jul 2018 19:59:02 +0200 From: Peter Zijlstra To: Guo Ren Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, daniel.lezcano@linaro.org, jason@lakedaemon.net, arnd@arndb.de, c-sky_gcc_upstream@c-sky.com, gnu-csky@mentor.com, thomas.petazzoni@bootlin.com, wbx@uclibc-ng.org, green.hu@gmail.com Subject: Re: [PATCH V2 11/19] csky: Atomic operations Message-ID: <20180705175902.GF2530@hirez.programming.kicks-ass.net> References: <860b8db036b33d7b3648cb1f4ec827a53dc1a01b.1530465326.git.ren_guo@c-sky.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <860b8db036b33d7b3648cb1f4ec827a53dc1a01b.1530465326.git.ren_guo@c-sky.com> 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 02, 2018 at 01:30:14AM +0800, Guo Ren wrote: > +static inline void arch_spin_lock(arch_spinlock_t *lock) > +{ > + unsigned int *p = &lock->lock; > + unsigned int tmp; > + > + asm volatile ( > + "1: ldex.w %0, (%1) \n" > + " bnez %0, 1b \n" > + " movi %0, 1 \n" > + " stex.w %0, (%1) \n" > + " bez %0, 1b \n" > + : "=&r" (tmp) > + : "r"(p) > + : "memory"); > + smp_mb(); > +} Test-and-set with MB acting as ACQUIRE, ok. > +static inline void arch_spin_unlock(arch_spinlock_t *lock) > +{ > + unsigned int *p = &lock->lock; > + unsigned int tmp; > + > + smp_mb(); > + asm volatile ( > + "1: ldex.w %0, (%1) \n" > + " movi %0, 0 \n" > + " stex.w %0, (%1) \n" > + " bez %0, 1b \n" > + : "=&r" (tmp) > + : "r"(p) > + : "memory"); > +} MB acting for RELEASE, but _why_ are you using a LDEX/STEX to clear the lock word? Would not a normal store work? Also, the fact that you need MB for release implies your LDEX does not in fact imply anything and your xchg/cmpxchg implementation is broken. > +static inline int arch_spin_trylock(arch_spinlock_t *lock) > +{ > + unsigned int *p = &lock->lock; > + unsigned int tmp; > + > + asm volatile ( > + "1: ldex.w %0, (%1) \n" > + " bnez %0, 2f \n" > + " movi %0, 1 \n" > + " stex.w %0, (%1) \n" > + " bez %0, 1b \n" > + " movi %0, 0 \n" > + "2: \n" > + : "=&r" (tmp) > + : "r"(p) > + : "memory"); > + smp_mb(); > + > + return !tmp; > +} Strictly speaking you can avoid the MB on failure. You only need to provide ACQUIRE semantics on success. That said, I would really suggest you implement a ticket lock instead of a test-and-set lock. They're not really all that complicated and do provide better worst case behaviour. > +/****** read lock/unlock/trylock ******/ Please have a look at using qrwlock -- esp. if you implement a ticket lock, then the rwlock comes for 'free'.