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 4AC4AC35242 for ; Tue, 11 Feb 2020 03:17:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A97C2080C for ; Tue, 11 Feb 2020 03:17:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="bwAyrzre" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727697AbgBKDRy (ORCPT ); Mon, 10 Feb 2020 22:17:54 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:48027 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727530AbgBKDRx (ORCPT ); Mon, 10 Feb 2020 22:17:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581391072; 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=7Nf36Pd4q2AVY4oKU24K8vx0+ORsf2vbbJBRG1witbM=; b=bwAyrzreQ8Yql56DYVIgWJokv1j48Pp1ppTjbDShUnb1/NvV/ydmZeAt63DhLsg956roKE QEL7UNOZx1GA2cFjbY2WeFPrLo7onnu+bOlUrxCgWOUqkPCRu4mRW5+7Hx5RpFoQycaw+H wkS2fCuzUFWKdJsZ/5UgQgcr6A7mL7k= 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-432-ryGiD3WYO_iQ5R0AcXlykw-1; Mon, 10 Feb 2020 22:17:48 -0500 X-MC-Unique: ryGiD3WYO_iQ5R0AcXlykw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 72832184AEB0; Tue, 11 Feb 2020 03:17:47 +0000 (UTC) Received: from [10.72.12.184] (ovpn-12-184.pek2.redhat.com [10.72.12.184]) by smtp.corp.redhat.com (Postfix) with ESMTP id 859ED83861; Tue, 11 Feb 2020 03:17:39 +0000 (UTC) Subject: Re: [PATCH v2 4/5] virtio-mmio: add MSI interrupt feature support To: Zha Bin , linux-kernel@vger.kernel.org Cc: virtio-dev@lists.oasis-open.org, slp@redhat.com, mst@redhat.com, jing2.liu@linux.intel.com, qemu-devel@nongnu.org, chao.p.peng@linux.intel.com, gerry@linux.alibaba.com References: <4c3d13be5a391b1fc50416838de57d903cbf8038.1581305609.git.zhabin@linux.alibaba.com> From: Jason Wang Message-ID: <0c71ff9d-1a7f-cfd2-e682-71b181bdeae4@redhat.com> Date: Tue, 11 Feb 2020 11:17:38 +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: <4c3d13be5a391b1fc50416838de57d903cbf8038.1581305609.git.zhabin@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 2020/2/10 =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 modern > 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 specifi= c > 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 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? Thanks