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=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 3B6BDC4338F for ; Thu, 5 Aug 2021 10:22:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 179A060724 for ; Thu, 5 Aug 2021 10:22:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240294AbhHEKXF (ORCPT ); Thu, 5 Aug 2021 06:23:05 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:3594 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240142AbhHEKXC (ORCPT ); Thu, 5 Aug 2021 06:23:02 -0400 Received: from fraeml734-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4GgPn36gKWz6F8JB; Thu, 5 Aug 2021 18:22:31 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml734-chm.china.huawei.com (10.206.15.215) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 5 Aug 2021 12:22:47 +0200 Received: from [10.47.24.8] (10.47.24.8) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Thu, 5 Aug 2021 11:22:46 +0100 Subject: Re: [PATCH] iommu/arm-smmu-v3: Remove some unneeded init in arm_smmu_cmdq_issue_cmdlist() To: , CC: , , , , References: <1624293394-202509-1-git-send-email-john.garry@huawei.com> From: John Garry Message-ID: Date: Thu, 5 Aug 2021 11:22:15 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: <1624293394-202509-1-git-send-email-john.garry@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.24.8] X-ClientProxiedBy: lhreml706-chm.china.huawei.com (10.201.108.55) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/06/2021 17:36, John Garry wrote: > Members of struct "llq" will be zero-inited, apart from member max_n_shift. > But we write llq.val straight after the init, so it was pointless to zero > init those other members. As such, separately init member max_n_shift > only. > > In addition, struct "head" is initialised to "llq" only so that member > max_n_shift is set. But that member is never referenced for "head", so > remove any init there. > > Removing these initializations is seen as a small performance optimisation, > as this code is (very) hot path. > Hi Will, Any chance you can pick up this small optimisation? Cheers > Signed-off-by: John Garry > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > index 54b2f27b81d4..8a8ad49bb7fd 100644 > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > @@ -727,11 +727,11 @@ static int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu, > unsigned long flags; > bool owner; > struct arm_smmu_cmdq *cmdq = &smmu->cmdq; > - struct arm_smmu_ll_queue llq = { > - .max_n_shift = cmdq->q.llq.max_n_shift, > - }, head = llq; > + struct arm_smmu_ll_queue llq, head; > int ret = 0; > > + llq.max_n_shift = cmdq->q.llq.max_n_shift; > + > /* 1. Allocate some space in the queue */ > local_irq_save(flags); > llq.val = READ_ONCE(cmdq->q.llq.val); >