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 0BE9BC76192 for ; Wed, 17 Jul 2019 08:59:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C84DE2077C for ; Wed, 17 Jul 2019 08:59:18 +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="TZHdWNwI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730463AbfGQI7R (ORCPT ); Wed, 17 Jul 2019 04:59:17 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:39132 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725948AbfGQI7R (ORCPT ); Wed, 17 Jul 2019 04:59:17 -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=vAzlqx/lFVlfT0a1qLbPZP1qhezVl/F0oinXuzJi9bw=; b=TZHdWNwIYTCWJ0RxqxfUHlLnY +VupZBhYjL0yeFleSwLYphjW1QXBSWIICBb+KSaGFTiwWOggj3RhUN625816vNXK7uoNQ47B+2ZpZ wMASf51aAidNJUjJ+canyxQaoERvd9jp756ri2gktddwKXCyNvopDH+wQB460WWdHHoVSvOP7v1VR e2nsKG+TkQxEkWjD68U6VLfpVVTmYpOtRZQ/f250DhY3iZlpAOjlOieTOTVH0597OeNRrz+xqvv1O lO/C1lxkKAek/pVup0GljJKgl1EqXJvyi+8pPEfKhaEd9ogK/lrInlgCOQ1BufObG8QxjtBhOdAQ+ GN5WjTSNA==; 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 Cc: linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, longman@redhat.com, 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: <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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190717083944.GR3463@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 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?