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=-5.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_NONE,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 DD596C47092 for ; Wed, 2 Jun 2021 04:38:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C481A61168 for ; Wed, 2 Jun 2021 04:38:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229701AbhFBEkY (ORCPT ); Wed, 2 Jun 2021 00:40:24 -0400 Received: from mga11.intel.com ([192.55.52.93]:28865 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229516AbhFBEkY (ORCPT ); Wed, 2 Jun 2021 00:40:24 -0400 IronPort-SDR: cPtzjus+TvFU7UGrYXUrbhfmrjdwHQvxPIeyydEudbKopFw8Ywv3wetgYQFeZ9W1HB850BiReb z75sYEkKphDg== X-IronPort-AV: E=McAfee;i="6200,9189,10002"; a="200688619" X-IronPort-AV: E=Sophos;i="5.83,241,1616482800"; d="scan'208";a="200688619" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jun 2021 21:38:36 -0700 IronPort-SDR: WnxDIDJVtYV3cqi62LfVUsTHx0jekxNgcPoporyzqfr3Kmq/YTcQXgtBigUP9h1PnoepDUO6vb CcHBzb8MVLZQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.83,241,1616482800"; d="scan'208";a="633098715" Received: from allen-box.sh.intel.com (HELO [10.239.159.105]) ([10.239.159.105]) by fmsmga006.fm.intel.com with ESMTP; 01 Jun 2021 21:38:34 -0700 Cc: baolu.lu@linux.intel.com, iommu@lists.linux-foundation.org, linuxarm@huawei.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 0/7] iommu: Allow IOVA rcache range be configured To: John Garry , joro@8bytes.org, will@kernel.org, robin.murphy@arm.com References: <1622557781-211697-1-git-send-email-john.garry@huawei.com> From: Lu Baolu Message-ID: <834ad35a-7310-1738-7d17-7c061ca73e4c@linux.intel.com> Date: Wed, 2 Jun 2021 12:37:20 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <1622557781-211697-1-git-send-email-john.garry@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/1/21 10:29 PM, John Garry wrote: > For streaming DMA mappings involving an IOMMU and whose IOVA len regularly > exceeds the IOVA rcache upper limit (meaning that they are not cached), > performance can be reduced. > > This is much more pronounced from commit 4e89dce72521 ("iommu/iova: Retry > from last rb tree node if iova search fails"), as discussed at [0]. > > IOVAs which cannot be cached are highly involved in the IOVA ageing issue, > as discussed at [1]. > > This series allows the IOVA rcache range be configured, so that we may > cache all IOVAs per domain, thus improving performance. > > A new IOMMU group sysfs file is added - max_opt_dma_size - which is used > indirectly to configure the IOVA rcache range: > /sys/kernel/iommu_groups/X/max_opt_dma_size > > This file is updated same as how the IOMMU group default domain type is > updated, i.e. must unbind the only device in the group first. Could you explain why it requires singleton group and driver unbinding if the user only wants to increase the upper limit? I haven't dived into the details yet, sorry if this is a silly question. Best regards, baolu