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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 7A5E6C433DB for ; Wed, 3 Mar 2021 13:10:04 +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 1ADCA601FF for ; Wed, 3 Mar 2021 13:10:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1ADCA601FF 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]:44434 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lHRGN-0006tR-4k for qemu-devel@archiver.kernel.org; Wed, 03 Mar 2021 08:10:03 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:46776) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lHRF8-0005t9-GL for qemu-devel@nongnu.org; Wed, 03 Mar 2021 08:08:46 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:41693) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lHRF6-0005Pu-Rc for qemu-devel@nongnu.org; Wed, 03 Mar 2021 08:08:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614776924; 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=oUoz2yPxM1iD68TTHMRZcqrcwChnyWydTeXmPIfN6HE=; b=YitI8fx5inDJFzmiGZyR5Q/+KKZNotjnBMyU/WjQkNBUIZeALhTdKqF2R8msNUcXOaBGAl v0X1Ds973JygxfuRzOg1XY4+rOlMqusTA2v4/RsPD1uTMyFbCuXs6jBDy9It1m4zEJIc7U syUll8SkKzli0FuXKutU7PrEEny+lDo= 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-364-mJdbe6QEMgix3COGZ-QOpg-1; Wed, 03 Mar 2021 08:08:40 -0500 X-MC-Unique: mJdbe6QEMgix3COGZ-QOpg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 223B58017FF for ; Wed, 3 Mar 2021 13:08:39 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-12-107.pek2.redhat.com [10.72.12.107]) by smtp.corp.redhat.com (Postfix) with ESMTP id 055A25D705; Wed, 3 Mar 2021 13:08:28 +0000 (UTC) Subject: Re: Inconsistent virtio-net-pci MSI vector count To: Stefan Hajnoczi References: From: Jason Wang Message-ID: Date: Wed, 3 Mar 2021 21:08:27 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB Received-SPF: pass client-ip=63.128.21.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, 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: qemu-devel@nongnu.org, "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2021/3/3 6:53 下午, Stefan Hajnoczi wrote: > Hi Jason, > I stumbled across something strange with virtio-net multi-queue today. > It doesn't seem to be a bug in practice, just an inconsistency. Here are > the details in case you think something needs to be changed: > > libvirt uses the vectors = 2 * N + 2 formula from > https://www.linux-kvm.org/page/Multiqueue to calculate the number of PCI > MSI vectors, where N is the number of rx/tx queue pairs. > > QEMU's virtio-net-pci device has 3 MSI vectors by default. This is > inconsistent with the formula that libvirt uses (should be 4 instead of > 3). Yes. > > Luckily, the Linux virtio_net.ko driver does not configure a callback > function for the control virtqueue. Therefore it can still use MSI with > only 3 vectors (config, rx, tx) instead of 4 (config, rx, tx, ctrl). > > But other driver implementations might need the ctrl vq vector and would > not have enough MSI vectors. > > Perhaps new QEMU machine types should set vectors to 4 by default? Or it's time to accept this: https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg01330.html Thanks > > Stefan