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=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 F09CDC76186 for ; Wed, 17 Jul 2019 08:59:05 +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 C49682077C for ; Wed, 17 Jul 2019 08:59:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="m7MycgEo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C49682077C 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-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject: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=T8gbpkDs/2aH8vXMOjk4GgommrFNCkBFMbWUaUats1A=; b=m7MycgEorm9P0V Sz88sF/TsKSHifvb22xiSkbJYRjdx+T/iaNGFkGVz+WtsbBITESP7nD8Ln03Vm5ABKFCznOartB/4 3Cc9+F2mUX2cFZJZhB/NBo6Oo8xG3FxkqZ5uNtq7eXU32STHyNhC8emoYcLJS95qAbp193rQnC48I 2KMvdHKwPBwa0W4ic3iS1+CrZKVkbMCtIev91cbcw2oqdQNadczWJHxRwMunzexh7VoGi8zgO3OSh dBPHVKgqgcc8OtImDVKuZQ23gruxjHU/fpRq/GWGDSMP1qRQDiPTXM2NWIabUcd7ZII1BRV9auE0Y En3F1h4LogmlaTu/5N2Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hnfmD-0001zu-96; Wed, 17 Jul 2019 08:59:05 +0000 Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hnfmA-0001zi-SN; Wed, 17 Jul 2019 08:59:03 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D667720B51F57; Wed, 17 Jul 2019 10:59:00 +0200 (CEST) Date: Wed, 17 Jul 2019 10:59:00 +0200 From: Peter Zijlstra To: Alex Kogan Subject: Re: [PATCH v3 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20190717085900.GS3463@hirez.programming.kicks-ass.net> References: <20190715192536.104548-1-alex.kogan@oracle.com> <20190715192536.104548-4-alex.kogan@oracle.com> <20190716155022.GR3419@hirez.programming.kicks-ass.net> <193BBB31-F376-451F-BDE1-D4807140EB51@oracle.com> <20190716184724.GH3402@hirez.programming.kicks-ass.net> <20190717083944.GR3463@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190717083944.GR3463@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, guohanjun@huawei.com, arnd@arndb.de, dave.dice@oracle.com, jglauber@marvell.com, x86@kernel.org, will.deacon@arm.com, linux@armlinux.org.uk, steven.sistare@oracle.com, linux-kernel@vger.kernel.org, rahul.x.yadav@oracle.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, longman@redhat.com, tglx@linutronix.de, daniel.m.jordan@oracle.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jul 17, 2019 at 10:39:44AM +0200, Peter Zijlstra wrote: > On Tue, Jul 16, 2019 at 08:47:24PM +0200, Peter Zijlstra wrote: > > My primary concern was readability; I find the above suggestion much > > more readable. Maybe it can be written differently; you'll have to play > > around a bit. > > static void cna_splice_tail(struct cna_node *cn, struct cna_node *head, struct cna_node *tail) > { > struct cna_node *list; > > /* remove [head,tail] */ > WRITE_ONCE(cn->mcs.next, tail->mcs.next); > tail->mcs.next = NULL; > > /* stick [head,tail] on the secondary list tail */ > if (cn->mcs.locked <= 1) { > /* create secondary list */ > head->tail = tail; > cn->mcs.locked = head->encoded_tail; > } else { > /* add to tail */ > list = (struct cna_node *)decode_tail(cn->mcs.locked); > list->tail->next = head; > list->tail = tail; > } > } > > static struct cna_node *cna_find_next(struct mcs_spinlock *node) > { > struct cna_node *cni, *cn = (struct cna_node *)node; > struct cna_node *head, *tail = NULL; > > /* find any next lock from 'our' node */ > for (head = cni = (struct cna_node *)READ_ONCE(cn->mcs.next); > cni && cni->node != cn->node; > tail = cni, cni = (struct cna_node *)READ_ONCE(cni->mcs.next)) > ; I think we can do away with those READ_ONCE()s, at this point those pointers should be stable. But please double check. > /* when found, splice any skipped locks onto the secondary list */ > if (cni && tail) > cna_splice_tail(cn, head, tail); > > return cni; > } > > How's that? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel