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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS 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 C29DDC433DF for ; Thu, 28 May 2020 15:37:08 +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 8DBAB207D3 for ; Thu, 28 May 2020 15:37:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Gh/Y7ayh" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8DBAB207D3 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]:50434 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jeKah-0002n8-K2 for qemu-devel@archiver.kernel.org; Thu, 28 May 2020 11:37:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60730) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jeKZz-0002Gv-IG for qemu-devel@nongnu.org; Thu, 28 May 2020 11:36:23 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:28555 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 1jeKZx-0002tB-R5 for qemu-devel@nongnu.org; Thu, 28 May 2020 11:36:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590680180; 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=RrC8XOAAJ4hwA9VETbSG4ZWJzMPgOgRTQKLSgMbR5hM=; b=Gh/Y7ayhCjY9vDhpR7UGCTZANuHQ2ELwaP6Cqc1Gde9bPqdHdkXhlQJyDBXVuMTXwKOnfC QLOiBPANHt8+VORGxWzpps//NT9guO/IITnZbte//whZ7ZsPROwn2hQaZ1ZsRypNU0GKjM +oGgTG+wOV06NDR/DUnx19v5Zv03M+A= 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-494-FKMgJkzoP7uqu7ga-8p4hQ-1; Thu, 28 May 2020 11:36:16 -0400 X-MC-Unique: FKMgJkzoP7uqu7ga-8p4hQ-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 4AD8B108BD1A; Thu, 28 May 2020 15:36:15 +0000 (UTC) Received: from gondolin (ovpn-113-28.ams2.redhat.com [10.36.113.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id D70A37A8D7; Thu, 28 May 2020 15:35:57 +0000 (UTC) Date: Thu, 28 May 2020 17:35:55 +0200 From: Cornelia Huck To: Stefan Hajnoczi Subject: Re: [PATCH v4 1/5] virtio-pci: add virtio_pci_optimal_num_queues() helper Message-ID: <20200528173555.5f079b70.cohuck@redhat.com> In-Reply-To: <20200527102925.128013-2-stefanha@redhat.com> References: <20200527102925.128013-1-stefanha@redhat.com> <20200527102925.128013-2-stefanha@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/28 06:31:20 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-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" , qemu-devel@nongnu.org, Max Reitz , Paolo Bonzini , Fam Zheng , Raphael Norwitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 27 May 2020 11:29:21 +0100 Stefan Hajnoczi wrote: > 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(+) That looks like a good idea, since the policy can be easily tweaked in one place later. For ccw, I don't see a good way to arrive at an optimal number of queues. Is there something we should do for mmio? If yes, should this be a callback in VirtioBusClass?