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,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 14C76C352A3 for ; Tue, 11 Feb 2020 07:40:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DCF52206D7 for ; Tue, 11 Feb 2020 07:40:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="K0PeafbE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727704AbgBKHkk (ORCPT ); Tue, 11 Feb 2020 02:40:40 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:36287 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727561AbgBKHkj (ORCPT ); Tue, 11 Feb 2020 02:40:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581406838; 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=ZjFU7GeDDGN0fIv5jKH93uf0oKdJEGFk6UYVtVN2y38=; b=K0PeafbE2RyuQYyqUbyNSZHUxcSyvteDiMjGcUwknfhogfrNZ88BUaIVTn05BOftNAD1DF FKUJA6Jj41BtpncRWqMAxhbVvImQlyYDsf6mV1eX5/lQg9QJ7oiXaFnYph/n3svn46eXm/ iQSRJHNZev6kDElymOmArKwuAQ+bqCc= 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-431-lfzle8XOMY-D_qcFc9LDBg-1; Tue, 11 Feb 2020 02:40:37 -0500 X-MC-Unique: lfzle8XOMY-D_qcFc9LDBg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E4B6A800D4E; Tue, 11 Feb 2020 07:40:35 +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 72C8B5D9CA; Tue, 11 Feb 2020 07:40:25 +0000 (UTC) Subject: Re: [virtio-dev] Re: [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support To: "Liu, Jing2" , Zha Bin , linux-kernel@vger.kernel.org Cc: virtio-dev@lists.oasis-open.org, slp@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, chao.p.peng@linux.intel.com, gerry@linux.alibaba.com References: <4c3d13be5a391b1fc50416838de57d903cbf8038.1581305609.git.zhabin@linux.alibaba.com> <0c71ff9d-1a7f-cfd2-e682-71b181bdeae4@redhat.com> <5522f205-207b-b012-6631-3cc77dde3bfe@linux.intel.com> From: Jason Wang Message-ID: <45e22435-08d3-08fe-8843-d8db02fcb8e3@redhat.com> Date: Tue, 11 Feb 2020 15:40:23 +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: <5522f205-207b-b012-6631-3cc77dde3bfe@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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=20 >>>>> using >>>>> virtio over mmio devices as a lightweight machine model for modern >>>>> cloud. The standard virtio over MMIO transport layer only supports=20 >>>>> one >>>>> legacy interrupt, which is much heavier than virtio over PCI=20 >>>>> transport >>>>> layer using MSI. Legacy interrupt has long work path and causes=20 >>>>> specific >>>>> VMExits in following cases, which would considerably slow down the >>>>> 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 feature >>>>> bit VIRTIO_F_MMIO_MSI[1] which increases the interrupt performance. >>>>> >>>>> With the VIRTIO_F_MMIO_MSI feature bit supported, the virtio-mmio M= SI >>>>> uses msi_sharing[1] to indicate the event and vector mapping. >>>>> Bit 1 is 0: device uses non-sharing and fixed vector per event=20 >>>>> 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=20 >>> queue >>> >>> (it wants msi vector sharing as name) and doesn't want a high=20 >>> 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=20 > SHOULD write a valid MsiVecSel followed by=20 > VIRTIO_MMIO_MSI_CMD_MAP_CONFIG/VIRTIO_MMIO_MSI_CMD_MAP_QUEUE command=20 > to map the configuration change/selected queue events respectively.=C2=A0= "=20 > (See spec patch 5/5) > > So if driver detects the msi sharing mode, when it does setup vq,=20 > writes the queue_sel (this already exists in setup vq), vector sel and=20 > 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 why=20 you need to introduce MSI_SHARING_MASK which is the charge of driver=20 instead of device. The interrupt rate should have no direct relationship=20 with whether it has been shared or not. Btw, you introduce mask/unmask without pending, how to deal with the=20 lost interrupt during the masking then? > For msi non-sharing mode, no special action is needed because we make=20 > the rule of per_vq_vector and fixed relationship. > > Correct me if this is not that clear for spec/code comments. > The ABI is not as straightforward as PCI did. Why not just reuse the PCI=20 layout? E.g having queue_sel queue_msix_vector msix_config for configuring map between msi vector and queues/config Then vector_sel address data pending mask unmask for configuring msi table? Thanks > Thanks! > > Jing > > >> >> ? >> >> Thanks >> >> >>> >>> >>>> Thanks >>>> >>>> >>>> >>>> --------------------------------------------------------------------= - >>>> To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org >>>> For additional commands, e-mail: virtio-dev-help@lists.oasis-open.or= g >>>> >>> >>