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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 36CADC76186 for ; Wed, 17 Jul 2019 07:45:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB04120818 for ; Wed, 17 Jul 2019 07:45:06 +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="YbNCb/0g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726212AbfGQHpG (ORCPT ); Wed, 17 Jul 2019 03:45:06 -0400 Received: from merlin.infradead.org ([205.233.59.134]:34856 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725890AbfGQHpF (ORCPT ); Wed, 17 Jul 2019 03:45:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To: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=a+w5j6eHYvJzioLr+1nRU4VPj/HkjhXiSU4Y9J8b7R8=; b=YbNCb/0gjQZL0XpBqEiPAwf+A9 3CgD9+vHlITW3ap2VMwt3sgVkwTzhRuRP/kgyZkGXM4XSu0z6A6ofUZh7f//Sux0TTeqwycROgOyW mLxn1uh9uXpCSJnqhfhbJdGj+v0bNg1lHzvz/yqDdsRlq+uKC9Ugrjw8MjS6FdMQsWpzu6XKr18uv WaT+N+4woH/KJYWFG573iBJIz5dq7RZjKNF11vp/WY7jPjvztxxaroPXOZPOogzOFYZazsr/lMDfq Cr6oTbCR8umH6TQpwxREIHsW/uUlzeCDHYQiMnCyPBHR0Af3bvNHEZk/DterF+Yju8ZMnXLDyTUoc J3NLOz9A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hnec8-0008Nx-I5; Wed, 17 Jul 2019 07:44:36 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 148B02059DEA3; Wed, 17 Jul 2019 09:44:35 +0200 (CEST) Date: Wed, 17 Jul 2019 09:44:35 +0200 From: Peter Zijlstra To: Waiman Long Cc: Alex Kogan , linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, x86@kernel.org, guohanjun@huawei.com, jglauber@marvell.com, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com Subject: Re: [PATCH v3 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20190717074435.GU3419@hirez.programming.kicks-ass.net> References: <20190715192536.104548-1-alex.kogan@oracle.com> <20190715192536.104548-4-alex.kogan@oracle.com> <9fa54e98-0b9b-0931-db32-c6bd6ccfe75b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9fa54e98-0b9b-0931-db32-c6bd6ccfe75b@redhat.com> 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 Tue, Jul 16, 2019 at 10:16:29PM -0400, Waiman Long wrote: > A simple graphic to illustrate those queues will help too, for example Very much yes! > /* >  * MCS lock holder >  * =============== >  *    mcs_node >  *   +--------+      +----+         +----+ >  *   | next   | ---> |next| -> ...  |next| -> NULL  [Main queue] >  *   | locked | -+   +----+         +----+ >  *   +--------+  | >  *               |   +----+         +----+ >  *               +-> |next| -> ...  |next| -> X     [Secondary queue] >  *    cna_node       +----+         +----+ >  *   +--------*                       ^ >  *   | tail   | ----------------------+ >  *   +--------*    Almost; IIUC that cna_node is the same as the one from locked, so you end up with something like: >  *    mcs_node >  *   +--------+      +----+         +----+ >  *   | next   | ---> |next| -> ...  |next| -> NULL  [Main queue] >  *   | locked | -+   +----+         +----+ >  *   +--------+  | >  *               |   +---------+         +----+ >  *               +-> |mcs::next| -> ...  |next| -> NULL     [Secondary queue] > * |cna::tail| -+ +----+ >  *          +---------+ | ^ > * +--------+ >  * >  * N.B. locked = 1 if secondary queue is absent. >  */