From nobody Fri Nov 14 22:08:58 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1590575467; cv=none; d=zohomail.com; s=zohoarc; b=hNB01Uwo7EdGw7ICGeJFwYc+ZHvO5Sxh22T5nLGI03CGLPijtM/LCTbxLwlPt7kn8M4W+buhB9Qo8IV/7lETBT8hhb552JSANqD+pwUqe2vdH+DXvd4jcA1raJpiprkLaPGZQNnzwLrvahFYGBZUOASXbkrxCJtkSeHR6fZkXMY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1590575467; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To; bh=QzfuoH281zyXLe3OPWvxcTWK2OHxNTXKDxKKnbkGlAs=; b=KMw5Lr4iQHqEUv2S5FORFkkwIb8DzNU1nvE/A186GMAjxhuJctBilyOpnDnd1JEqQnDjC4TdGbplSc4w7UDk1L0Oa/bVHI+iGPUsM5s1COm3u/rlspQn9eQarLupk3fRgtBq+mLZi4JBPyABroxKg8BGU+dbjj7UtxAxo1TOP7Q= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1590575467536548.6198994665386; Wed, 27 May 2020 03:31:07 -0700 (PDT) Received: from localhost ([::1]:37364 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jdtL0-0008UM-4E for importer@patchew.org; Wed, 27 May 2020 06:31:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55838) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jdtJg-0006p3-2h for qemu-devel@nongnu.org; Wed, 27 May 2020 06:29:44 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:48924 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jdtJf-00011L-71 for qemu-devel@nongnu.org; Wed, 27 May 2020 06:29:43 -0400 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-91-TD_f2IsLO8iujHOjnreCOA-1; Wed, 27 May 2020 06:29:41 -0400 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 92FB680183C; Wed, 27 May 2020 10:29:39 +0000 (UTC) Received: from localhost (ovpn-114-250.ams2.redhat.com [10.36.114.250]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0ADF46C77F; Wed, 27 May 2020 10:29:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590575382; 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=QzfuoH281zyXLe3OPWvxcTWK2OHxNTXKDxKKnbkGlAs=; b=QhYV+CQGS/gWM4fLwn+UWjlentJyTZETkjY8SxzBvh4rOemeJ2vgL1aDEdoBaoS0CwjBI7 DDSz7iEsCzep9Rrh64rvSGgoAI4+bfJbgt/6LCrdmETai+jqqBwpb7v/j0+iPheey+QgVG +96tG4r4AlZXLAQ34nJjoMpc693Wpic= X-MC-Unique: TD_f2IsLO8iujHOjnreCOA-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH v4 1/5] virtio-pci: add virtio_pci_optimal_num_queues() helper Date: Wed, 27 May 2020 11:29:21 +0100 Message-Id: <20200527102925.128013-2-stefanha@redhat.com> In-Reply-To: <20200527102925.128013-1-stefanha@redhat.com> References: <20200527102925.128013-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=207.211.31.81; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 00:45:05 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -3 X-Spam_score: -0.4 X-Spam_bar: / X-Spam_report: (-0.4 / 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, MIME_BASE64_TEXT=1.741, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , Pankaj Gupta , Eduardo Habkost , qemu-block@nongnu.org, "Michael S. Tsirkin" , cohuck@redhat.com, Max Reitz , Stefan Hajnoczi , Paolo Bonzini , Fam Zheng , Raphael Norwitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Multi-queue devices achieve the best performance when each vCPU has a dedicated queue. This ensures that virtqueue used notifications are handled on the same vCPU that submitted virtqueue buffers. When another vCPU handles the the notification an IPI will be necessary to wake the submission vCPU and this incurs a performance overhead. Provide a helper function that virtio-pci devices will use in later patches to automatically select the optimal number of queues. Signed-off-by: Stefan Hajnoczi --- hw/virtio/virtio-pci.h | 9 +++++++++ hw/virtio/virtio-pci.c | 7 +++++++ 2 files changed, 16 insertions(+) diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h index e2eaaa9182..91096f0291 100644 --- a/hw/virtio/virtio-pci.h +++ b/hw/virtio/virtio-pci.h @@ -243,4 +243,13 @@ typedef struct VirtioPCIDeviceTypeInfo { /* Register virtio-pci type(s). @t must be static. */ void virtio_pci_types_register(const VirtioPCIDeviceTypeInfo *t); =20 +/** + * virtio_pci_optimal_num_queues: + * @fixed_queues: number of queues that are always present + * + * Returns: The optimal number of queues for a multi-queue device, excludi= ng + * @fixed_queues. + */ +unsigned virtio_pci_optimal_num_queues(unsigned fixed_queues); + #endif diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c index d028c17c24..0c4f0100ca 100644 --- a/hw/virtio/virtio-pci.c +++ b/hw/virtio/virtio-pci.c @@ -19,6 +19,7 @@ =20 #include "exec/memop.h" #include "standard-headers/linux/virtio_pci.h" +#include "hw/boards.h" #include "hw/virtio/virtio.h" #include "migration/qemu-file-types.h" #include "hw/pci/pci.h" @@ -2024,6 +2025,12 @@ void virtio_pci_types_register(const VirtioPCIDevice= TypeInfo *t) g_free(base_name); } =20 +unsigned virtio_pci_optimal_num_queues(unsigned fixed_queues) +{ + /* 1:1 vq to vcpu mapping is ideal because it avoids IPIs */ + return MIN(current_machine->smp.cpus, VIRTIO_QUEUE_MAX - fixed_queues); +} + /* virtio-pci-bus */ =20 static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size, --=20 2.25.4