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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 A8774C433DF for ; Thu, 27 Aug 2020 19:41:45 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 6B60720714 for ; Thu, 27 Aug 2020 19:41:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B60720714 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 38C8D87D09; Thu, 27 Aug 2020 19:41:45 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id uX2QBmQKbsGV; Thu, 27 Aug 2020 19:41:43 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id 02403875DA; Thu, 27 Aug 2020 19:41:42 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id D62F4C016F; Thu, 27 Aug 2020 19:41:42 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id CEB45C0051 for ; Thu, 27 Aug 2020 19:41:41 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id A37BE203E8 for ; Thu, 27 Aug 2020 19:41:41 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id U2ERYlaH+Liu for ; Thu, 27 Aug 2020 19:41:39 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by silver.osuosl.org (Postfix) with ESMTP id C8AA62038A for ; Thu, 27 Aug 2020 19:41:39 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 82D0931B; Thu, 27 Aug 2020 12:41:38 -0700 (PDT) Received: from [10.57.40.122] (unknown [10.57.40.122]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CD8DC3F68F; Thu, 27 Aug 2020 12:41:37 -0700 (PDT) Subject: Re: [PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova To: Shaokun Zhang , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <1598517834-30275-1-git-send-email-zhangshaokun@hisilicon.com> From: Robin Murphy Message-ID: <3afcc7b2-0bfb-b79c-513f-1beb66c5f164@arm.com> Date: Thu, 27 Aug 2020 20:41:36 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <1598517834-30275-1-git-send-email-zhangshaokun@hisilicon.com> Content-Language: en-GB Cc: Yuqi Jin X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 2020-08-27 09:43, Shaokun Zhang wrote: > From: Yuqi Jin > > The performance of the atomic_xchg is better than atomic_cmpxchg because > no comparison is required. While the value of @fq_timer_on can only be 0 > or 1. Let's use atomic_xchg instead of atomic_cmpxchg here because we > only need to check that the value changes from 0 to 1 or from 1 to 1. Looks reasonable to me - the "compare" part is already covered by the separate atomic_read(), and as you say there's no harm if the "exchange" part races as long as it's still atomic. Reviewed-by: Robin Murphy > Cc: Joerg Roedel > Signed-off-by: Yuqi Jin > Signed-off-by: Shaokun Zhang > --- > drivers/iommu/iova.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index 45a251da5453..30d969a4c5fd 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -579,7 +579,7 @@ void queue_iova(struct iova_domain *iovad, > > /* Avoid false sharing as much as possible. */ > if (!atomic_read(&iovad->fq_timer_on) && > - !atomic_cmpxchg(&iovad->fq_timer_on, 0, 1)) > + !atomic_xchg(&iovad->fq_timer_on, 1)) > mod_timer(&iovad->fq_timer, > jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); > } > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu