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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 5265AC352A3 for ; Tue, 11 Feb 2020 12:05:21 +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 1FC962051A for ; Tue, 11 Feb 2020 12:05:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="L3K+9Jwu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1FC962051A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48464 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1UI4-0000eE-Aj for qemu-devel@archiver.kernel.org; Tue, 11 Feb 2020 07:05:20 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:50809) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1UHS-00009M-A2 for qemu-devel@nongnu.org; Tue, 11 Feb 2020 07:04:43 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j1UHQ-00030x-Ov for qemu-devel@nongnu.org; Tue, 11 Feb 2020 07:04:41 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:54786 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j1UHQ-00030a-K4 for qemu-devel@nongnu.org; Tue, 11 Feb 2020 07:04:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581422679; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SjQwrMmKYTsdFrSHKfW1siyerTxdkA/ZJqrqrVqTmls=; b=L3K+9JwurkdYuIkDUa6cQrRijWsW9CWlsn71peAXp7lEba0NN7U9KSwrDv3QrKkWqWEpWh 2+GPvsdeptwazWkBa5rW9lnglJmhI1L71H79nrIk4OmWkfr106ZM15Di8+W7sb2qaheBRk fajrFPBUnnb/jDcJHM92503SP3U6A2E= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-328-070av-dGNxCVVe93W4fnVw-1; Tue, 11 Feb 2020 07:04:36 -0500 X-MC-Unique: 070av-dGNxCVVe93W4fnVw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9A383107ACC9; Tue, 11 Feb 2020 12:04:34 +0000 (UTC) Received: from [10.72.13.150] (ovpn-13-150.pek2.redhat.com [10.72.13.150]) by smtp.corp.redhat.com (Postfix) with ESMTP id 56C6960BF4; Tue, 11 Feb 2020 12:04:25 +0000 (UTC) Subject: Re: [virtio-dev] Re: [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support To: "Michael S. Tsirkin" References: <4c3d13be5a391b1fc50416838de57d903cbf8038.1581305609.git.zhabin@linux.alibaba.com> <0c71ff9d-1a7f-cfd2-e682-71b181bdeae4@redhat.com> <5522f205-207b-b012-6631-3cc77dde3bfe@linux.intel.com> <45e22435-08d3-08fe-8843-d8db02fcb8e3@redhat.com> <20200211065319-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Tue, 11 Feb 2020 20:04:24 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20200211065319-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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: virtio-dev@lists.oasis-open.org, Zha Bin , slp@redhat.com, "Liu, Jing2" , linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, chao.p.peng@linux.intel.com, gerry@linux.alibaba.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/2/11 =E4=B8=8B=E5=8D=887:58, Michael S. Tsirkin wrote: > On Tue, Feb 11, 2020 at 03:40:23PM +0800, Jason Wang wrote: >> On 2020/2/11 =E4=B8=8B=E5=8D=882:02, Liu, Jing2 wrote: >>> On 2/11/2020 12:02 PM, Jason Wang wrote: >>>> On 2020/2/11 =E4=B8=8A=E5=8D=8811:35, Liu, Jing2 wrote: >>>>> On 2/11/2020 11:17 AM, Jason Wang wrote: >>>>>> On 2020/2/10 =E4=B8=8B=E5=8D=885:05, Zha Bin wrote: >>>>>>> From: Liu Jiang >>>>>>> >>>>>>> Userspace VMMs (e.g. Qemu microvm, Firecracker) take >>>>>>> advantage of using >>>>>>> virtio over mmio devices as a lightweight machine model for moder= n >>>>>>> cloud. The standard virtio over MMIO transport layer >>>>>>> only supports one >>>>>>> legacy interrupt, which is much heavier than virtio over >>>>>>> PCI transport >>>>>>> layer using MSI. Legacy interrupt has long work path and >>>>>>> causes specific >>>>>>> VMExits in following cases, which would considerably slow down th= e >>>>>>> performance: >>>>>>> >>>>>>> 1) read interrupt status register >>>>>>> 2) update interrupt status register >>>>>>> 3) write IOAPIC EOI register >>>>>>> >>>>>>> We proposed to add MSI support for virtio over MMIO via new featu= re >>>>>>> bit VIRTIO_F_MMIO_MSI[1] which increases the interrupt performanc= e. >>>>>>> >>>>>>> With the VIRTIO_F_MMIO_MSI feature bit supported, the virtio-mmio= MSI >>>>>>> uses msi_sharing[1] to indicate the event and vector mapping. >>>>>>> Bit 1 is 0: device uses non-sharing and fixed vector per >>>>>>> event mapping. >>>>>>> Bit 1 is 1: device uses sharing mode and dynamic mapping. >>>>>> I believe dynamic mapping should cover the case of fixed vector? >>>>>> >>>>> Actually this bit*aims* for msi sharing or msi non-sharing. >>>>> >>>>> It means, when msi sharing bit is 1, device doesn't want vector >>>>> per queue >>>>> >>>>> (it wants msi vector sharing as name) and doesn't want a high >>>>> interrupt rate. >>>>> >>>>> So driver turns to !per_vq_vectors and has to do dynamical mapping. >>>>> >>>>> So they are opposite not superset. >>>>> >>>>> Thanks! >>>>> >>>>> Jing >>>> I think you need add more comments on the command. >>>> >>>> E.g if I want to map vector 0 to queue 1, how do I need to do? >>>> >>>> write(1, queue_sel); >>>> write(0, vector_sel); >>> That's true. Besides, two commands are used for msi sharing mode, >>> >>> VIRTIO_MMIO_MSI_CMD_MAP_CONFIG and VIRTIO_MMIO_MSI_CMD_MAP_QUEUE. >>> >>> "To set up the event and vector mapping for MSI sharing mode, driver >>> SHOULD write a valid MsiVecSel followed by >>> VIRTIO_MMIO_MSI_CMD_MAP_CONFIG/VIRTIO_MMIO_MSI_CMD_MAP_QUEUE command = to >>> map the configuration change/selected queue events respectively.=C2=A0= " (See >>> spec patch 5/5) >>> >>> So if driver detects the msi sharing mode, when it does setup vq, wri= tes >>> the queue_sel (this already exists in setup vq), vector sel and then >>> MAP_QUEUE command to do the queue event mapping. >>> >> So actually the per vq msix could be done through this. I don't get wh= y you >> need to introduce MSI_SHARING_MASK which is the charge of driver inste= ad of >> device. The interrupt rate should have no direct relationship with whe= ther >> it has been shared or not. >> >> Btw, you introduce mask/unmask without pending, how to deal with the l= ost >> interrupt during the masking then? > pending can be an internal device register. as long as device > does not lose interrupts while masked, all's well. You meant raise the interrupt during unmask automatically? > > There's value is being able to say "this queue sends no > interrupts do not bother checking used notification area". > so we need way to say that. So I guess an enable interrupts > register might have some value... > But besides that, it's enough to have mask/unmask/address/data > per vq. Just to check, do you mean "per vector" here? Thanks > >