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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E2A9EC433EF for ; Wed, 20 Oct 2021 07:31:39 +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 79545610FF for ; Wed, 20 Oct 2021 07:31:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 79545610FF 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-Transfer-Encoding:Content-Type: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=2GcUOSSaerjj9hAJnw7uMV7uVAyr2+lKvJpuEsL/G6o=; b=uaf4RPsrsJn0TcsKWYORCoaCp5 7/KsBE8H6QEdBJvIe7Qnr8zcUlyx/cDWwsp3P6+k52rQJkixsfUec46G7LapadsP/PlWltOFtqJVo hiyXZJtyPQHfC+YfO72wITOyTmB7zwzrZVIPfv2/3sRL5jbSUPrOvYvxWqmAVKVqEFQW1+R/HB6Qi 3LkqhAQ58p8pZbf7JqCBMYNgusKQUAmRRrU02EEPYqH8xjEPAaEhzj4yJFwWVQW1taYS/5J9uI3ok m3HEEfCknL54EZJ47u7qg37wB7TZyx92rJ7fPqG5n5RXm/NvVGC16q/sXb2jbtGQgIxSHcGi3Bfva VTejGOHw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1md634-003eSv-48; Wed, 20 Oct 2021 07:30:06 +0000 Received: from szxga01-in.huawei.com ([45.249.212.187]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1md62y-003eQJ-Aj for linux-arm-kernel@lists.infradead.org; Wed, 20 Oct 2021 07:30:02 +0000 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4HZ2Fb3VL3zbnKC; Wed, 20 Oct 2021 15:25:23 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggemv711-chm.china.huawei.com (10.1.198.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Wed, 20 Oct 2021 15:29:56 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Wed, 20 Oct 2021 15:29:56 +0800 Subject: Re: [PATCH v2 2/2] iommu/arm-smmu-v3: Simplify useless instructions in arm_smmu_cmdq_build_cmd() To: Will Deacon CC: Robin Murphy , Joerg Roedel , linux-arm-kernel , iommu , , "John Garry" References: <20210818080452.2079-1-thunder.leizhen@huawei.com> <20210818080452.2079-3-thunder.leizhen@huawei.com> <20211004120714.GD27373@willie-the-truck> From: "Leizhen (ThunderTown)" Message-ID: <68742c41-8610-9b3f-49b7-7ae04dc87ec2@huawei.com> Date: Wed, 20 Oct 2021 15:29:44 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20211004120714.GD27373@willie-the-truck> Content-Language: en-US X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211020_003000_813654_70633E6D X-CRM114-Status: GOOD ( 23.72 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2021/10/4 20:07, Will Deacon wrote: > On Wed, Aug 18, 2021 at 04:04:52PM +0800, Zhen Lei wrote: >> Although the parameter 'cmd' is always passed by a local array variable, >> and only this function modifies it, the compiler does not know this. The >> compiler almost always reads the value of cmd[i] from memory rather than >> directly using the value cached in the register. This generates many >> useless instruction operations and affects the performance to some extent. >> >> To guide the compiler for proper optimization, 'cmd' is defined as a local >> array variable, marked as register, and copied to the output parameter at >> a time when the function is returned. >> >> The optimization effect can be viewed by running the "size arm-smmu-v3.o" >> command. >> >> Before: >> text data bss dec hex >> 26954 1348 56 28358 6ec6 >> >> After: >> text data bss dec hex >> 26762 1348 56 28166 6e06 >> >> Signed-off-by: Zhen Lei >> --- >> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 11 ++++++++--- >> 1 file changed, 8 insertions(+), 3 deletions(-) >> >> 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 01e95b56ffa07d1..7cec0c967f71d86 100644 >> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >> @@ -234,10 +234,12 @@ static int queue_remove_raw(struct arm_smmu_queue *q, u64 *ent) >> } >> >> /* High-level queue accessors */ >> -static int arm_smmu_cmdq_build_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent) >> +static int arm_smmu_cmdq_build_cmd(u64 *out_cmd, struct arm_smmu_cmdq_ent *ent) >> { >> - memset(cmd, 0, 1 << CMDQ_ENT_SZ_SHIFT); >> - cmd[0] |= FIELD_PREP(CMDQ_0_OP, ent->opcode); >> + register u64 cmd[CMDQ_ENT_DWORDS]; > > 'register' is pretty badly specified outside of a handful of limited uses in > conjunction with inline asm, so I really don't think we should be using it > here. OK, I think I was overly aggressive in the beginning, and I just tried to remove the register modifier and get the same optimization. > >> + cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode); > > This generates a compiler warning about taking the address of a 'register' > variable. > > Will > . > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel