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=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 41532C4338F for ; Thu, 5 Aug 2021 15:18:35 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 0C9AF60EEA for ; Thu, 5 Aug 2021 15:18:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0C9AF60EEA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:CC:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=fXWJ/qdquFGgsErnJlajeankBpObqShWsKr/qEKxmHU=; b=3OuIDMugff6nGeCgraCUh3crP0 NFtUQVeCDyhJlz7UMXhontHlLfe9BvpEglKPY8Ht3LdRsSGPFRj6v7/yuC3iT6hJYk13Eex8BC2Tw pps9ifvEYFyEotwmQq94UWBiHkBummYHoDB+VfrpikMNnAJlGIAJAUcIbYDQSZX+mb2JBFkXHW77n OmbEXaBjQMX+EnihuYVRcsM/LOFnfzfMQZ1J0rAxwcGBGnH83T8uz4m5W8tPGCpV5u9qQtnBM7JAP 9Wv94/v+fhzVOvxWz2SQZ7vXTE/oaQ//Yq53ZjTqswW14Fv8yCgxZMFFTjzBh8d4WLP3qkoDX0A7S uvA1ixxw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mBf6y-00A23j-0F; Thu, 05 Aug 2021 15:16:44 +0000 Received: from frasgout.his.huawei.com ([185.176.79.56]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mBf6t-00A22Y-RR for linux-arm-kernel@lists.infradead.org; Thu, 05 Aug 2021 15:16:41 +0000 Received: from fraeml734-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4GgXJ01DVKz6F8Wk; Thu, 5 Aug 2021 23:16:16 +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 17:16:34 +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 16:16:33 +0100 Subject: Re: [PATCH] iommu/arm-smmu-v3: Remove some unneeded init in arm_smmu_cmdq_issue_cmdlist() To: Robin Murphy , CC: , , , , References: <1624293394-202509-1-git-send-email-john.garry@huawei.com> <45a8af4f-4202-ecd8-0882-507acf9b2eb2@huawei.com> <577a625a-4fc5-7402-8e4f-4e0e5be93144@arm.com> From: John Garry Message-ID: <44c5e07b-e663-5b96-a142-ec25666e2a14@huawei.com> Date: Thu, 5 Aug 2021 16:16:02 +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: <577a625a-4fc5-7402-8e4f-4e0e5be93144@arm.com> Content-Language: en-US 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210805_081640_091158_3A8CCA8B X-CRM114-Status: GOOD ( 17.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 05/08/2021 15:41, Robin Murphy wrote: >> I suppose they could be combined into a smaller sub-struct and loaded >> in a single operation, but it looks messy, and prob without much gain. > > Indeed I wouldn't say that saving memory is the primary concern here, > and any more convoluted code is hardly going to help performance. Plus > it still wouldn't help the other cases where we're just copying the size > into a fake queue to do some prod arithmetic - I hadn't fully clocked > what was going on there when I skimmed through things earlier. > > Disregarding the bogus layout change, though, do you reckon the rest of > my idea makes sense? I tried the similar change to avoid zero-init the padding in arm_smmu_cmdq_write_entries() and the _arm_smmu_cmdq_poll_set_valid_map(), but the disassembly was the same. So the compiler must have got smart there. But for the original change in this patch, it did make a difference. It's nice to remove what was a memcpy: 1770: a9077eff stp xzr, xzr, [x23, #112] }, head = llq; 1774: 94000000 bl 0 And performance was very fractionally better. As for pre-evaluating "nents", I'm not sure how much that can help, but I am not too optimistic. I can try some testing when I get a chance. Having said that, I would need to check the disassembly also. Thanks, John _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel