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=-2.5 required=3.0 tests=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 7E3E1C46470 for ; Wed, 8 Aug 2018 10:24:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 37DD5208C3 for ; Wed, 8 Aug 2018 10:24:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 37DD5208C3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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 S1727058AbeHHMnA (ORCPT ); Wed, 8 Aug 2018 08:43:00 -0400 Received: from foss.arm.com ([217.140.101.70]:36802 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726921AbeHHMnA (ORCPT ); Wed, 8 Aug 2018 08:43:00 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A51EF18A; Wed, 8 Aug 2018 03:23:57 -0700 (PDT) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 75E383F2EA; Wed, 8 Aug 2018 03:23:57 -0700 (PDT) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id CEA991AE180A; Wed, 8 Aug 2018 11:24:01 +0100 (BST) Date: Wed, 8 Aug 2018 11:24:01 +0100 From: Will Deacon To: Waiman Long Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Joe Mario , Davidlohr Bueso Subject: Re: [PATCH v3] locking/rwsem: Exit read lock slowpath if queue empty & no writer Message-ID: <20180808102401.GC28557@arm.com> References: <1532459425-19204-1-git-send-email-longman@redhat.com> <55866c24-ff40-22cb-1390-6c9055bd2cb7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55866c24-ff40-22cb-1390-6c9055bd2cb7@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Waiman, On Tue, Aug 07, 2018 at 07:29:49PM -0400, Waiman Long wrote: > On 07/24/2018 03:10 PM, Waiman Long wrote: > > diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c > > index 3064c50..01fcb80 100644 > > --- a/kernel/locking/rwsem-xadd.c > > +++ b/kernel/locking/rwsem-xadd.c > > @@ -233,8 +233,19 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem, > > waiter.type = RWSEM_WAITING_FOR_READ; > > > > raw_spin_lock_irq(&sem->wait_lock); > > - if (list_empty(&sem->wait_list)) > > + if (list_empty(&sem->wait_list)) { > > + /* > > + * In case the wait queue is empty and the lock isn't owned > > + * by a writer, this reader can exit the slowpath and return > > + * immediately as its RWSEM_ACTIVE_READ_BIAS has already > > + * been set in the count. > > + */ > > + if (atomic_long_read(&sem->count) >= 0) { > > + raw_spin_unlock_irq(&sem->wait_lock); > > + return sem; > > + } > > adjustment += RWSEM_WAITING_BIAS; > > + } > > list_add_tail(&waiter.list, &sem->wait_list); > > > > /* we're now waiting on the lock, but no longer actively locking */ > > Will this patch be eligible to go into 4.19 or 4.20? It's probably worth reposting with the Acks you've received, so that Ingo can easily pick it up into -tip (but it might be a bit close for 4.19 at this point). Will