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=-5.3 required=3.0 tests=BAYES_00, 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 4C8B5C433E0 for ; Thu, 18 Mar 2021 12:32:13 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 79D0564F4D for ; Thu, 18 Mar 2021 12:32:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 79D0564F4D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57250 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lMrox-0007GZ-Hx for qemu-devel@archiver.kernel.org; Thu, 18 Mar 2021 08:32:11 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57622) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lMrln-0004Cx-Uf for qemu-devel@nongnu.org; Thu, 18 Mar 2021 08:28:55 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:2070) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lMrlk-0001aD-Bu for qemu-devel@nongnu.org; Thu, 18 Mar 2021 08:28:55 -0400 Received: from DGGEMM405-HUB.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4F1R9J2lLszRRQ7; Thu, 18 Mar 2021 20:27:00 +0800 (CST) Received: from dggema765-chm.china.huawei.com (10.1.198.207) by DGGEMM405-HUB.china.huawei.com (10.3.20.213) with Microsoft SMTP Server (TLS) id 14.3.498.0; Thu, 18 Mar 2021 20:28:45 +0800 Received: from [10.174.185.210] (10.174.185.210) by dggema765-chm.china.huawei.com (10.1.198.207) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2106.2; Thu, 18 Mar 2021 20:28:45 +0800 Subject: Re: [RFC PATCH 0/3] vfio/migration: Support manual clear vfio dirty log To: "Tian, Kevin" , Alex Williamson , "Michael S . Tsirkin" , Cornelia Huck , Paolo Bonzini , "Kirti Wankhede" , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , Tarun Gupta , "open list:All patches CC here" References: <20210310094106.2191-1-jiangkunkun@huawei.com> From: Kunkun Jiang Message-ID: Date: Thu, 18 Mar 2021 20:28:33 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.174.185.210] X-ClientProxiedBy: dggeme718-chm.china.huawei.com (10.1.199.114) To dggema765-chm.china.huawei.com (10.1.198.207) X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.188; envelope-from=jiangkunkun@huawei.com; helo=szxga02-in.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "shameerali.kolothum.thodi@huawei.com" , Eric Auger , Peter Xu , Zenghui Yu , "wanghaibin.wang@huawei.com" , Keqian Zhu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Kevin, On 2021/3/18 17:04, Tian, Kevin wrote: >> From: Kunkun Jiang >> Sent: Thursday, March 18, 2021 3:59 PM >> >> Hi Kevin, >> >> On 2021/3/18 14:28, Tian, Kevin wrote: >>>> From: Kunkun Jiang >>>> Sent: Wednesday, March 10, 2021 5:41 PM >>>> >>>> Hi all, >>>> >>>> In the past, we clear dirty log immediately after sync dirty log to >>>> userspace. This may cause redundant dirty handling if userspace >>>> handles dirty log iteratively: >>>> >>>> After vfio clears dirty log, new dirty log starts to generate. These >>>> new dirty log will be reported to userspace even if they are generated >>>> before userspace handles the same dirty page. >>>> >>>> Since a new dirty log tracking method for vfio based on iommu hwdbm[1] >>>> has been introduced in the kernel and added a new capability named >>>> VFIO_DIRTY_LOG_MANUAL_CLEAR, we can eliminate some redundant >> dirty >>>> handling by supporting it. >>> Is there any performance data showing the benefit of this new method? >>> >> Current dirty log tracking method for VFIO: >> [1] All pages marked dirty if not all iommu_groups have pinned_scope >> [2] pinned pages by various vendor drivers if all iommu_groups have >> pinned scope >> >> Both methods are coarse-grained and can not determine which pages are >> really dirty. Each round may mark the pages that are not really dirty as >> dirty >> and send them to the destination. ( It might be better if the range of the >> pinned_scope was smaller. ) This will result in a waste of resources. >> >> HWDBM is short for Hardware Dirty Bit Management. >> (e.g. smmuv3 HTTU, Hardware Translation Table Update) >> >> About SMMU HTTU: >> HTTU is a feature of ARM SMMUv3, it can update access flag or/and dirty >> state of the TTD (Translation Table Descriptor) by hardware. >> >> With HTTU, stage1 TTD is classified into 3 types: >>                                  DBM bit AP[2](readonly bit) >> 1. writable_clean          1                            1 >> 2. writable_dirty           1                            0 >> 3. readonly                   0                            1 >> >> If HTTU_HD (manage dirty state) is enabled, smmu can change TTD from >> writable_clean to writable_dirty. Then software can scan TTD to sync dirty >> state into dirty bitmap. With this feature, we can track the dirty log of >> DMA continuously and precisely. >> >> The capability of VFIO_DIRTY_LOG_MANUAL_CLEAR is similar to that on >> the KVM side. We add this new log_clear() interface only to split the old >> log_sync() into two separated procedures: >> >> - use log_sync() to collect the collection only, and, >> - use log_clear() to clear the dirty bitmap. >> >> If you're interested in this new method, you can take a look at our set of >> patches. >> [1] >> https://lore.kernel.org/linux-iommu/20210310090614.26668-1- >> zhukeqian1@huawei.com/ >> > I know what you are doing. Intel is also working on VT-d dirty bit support > based on above link. What I'm curious is the actual performance gain > with this optimization. KVM doing that is one good reference, but IOMMU > has different characteristics (e.g. longer invalidation latency) compared to > CPU MMU. It's always good to understand what a so-called optimization > can actually optimize in a context different from where it's originally proved.😊 > > Thanks > Kevin My understanding is that this is a new method, which is quite different from the previous two. So can you explain in more detail what performance data you want?😁 Thanks, Kunkun Jiang