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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 EE977C3A5A2 for ; Thu, 22 Aug 2019 09:20:18 +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 C65F7233A0 for ; Thu, 22 Aug 2019 09:20:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C65F7233A0 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]:39550 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0jGT-0003vm-2M for qemu-devel@archiver.kernel.org; Thu, 22 Aug 2019 05:20:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44304) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0jFf-0003BC-Ar for qemu-devel@nongnu.org; Thu, 22 Aug 2019 05:19:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i0jFe-0004Lm-3U for qemu-devel@nongnu.org; Thu, 22 Aug 2019 05:19:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51882) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i0jFd-0004LF-SD for qemu-devel@nongnu.org; Thu, 22 Aug 2019 05:19:26 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6C17E85545 for ; Thu, 22 Aug 2019 09:19:24 +0000 (UTC) Received: from gondolin (dhcp-192-222.str.redhat.com [10.33.192.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id F21F75888; Thu, 22 Aug 2019 09:19:18 +0000 (UTC) Date: Thu, 22 Aug 2019 11:19:16 +0200 From: Cornelia Huck To: Stefan Hajnoczi Message-ID: <20190822111916.735fd3ce.cohuck@redhat.com> In-Reply-To: <20190822085237.GA20491@stefanha-x1.localdomain> References: <20190816143321.20903-1-dgilbert@redhat.com> <20190816143321.20903-2-dgilbert@redhat.com> <20190818065944-mutt-send-email-mst@kernel.org> <20190821191118.GN3309@work-vm> <20190822085237.GA20491@stefanha-x1.localdomain> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 22 Aug 2019 09:19:24 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 1/2] virtio: add vhost-user-fs base device 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: "Michael S. Tsirkin" , "Dr. David Alan Gilbert" , vgoyal@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 22 Aug 2019 09:52:37 +0100 Stefan Hajnoczi wrote: > On Wed, Aug 21, 2019 at 08:11:18PM +0100, Dr. David Alan Gilbert wrote: > > * Michael S. Tsirkin (mst@redhat.com) wrote: > > > On Fri, Aug 16, 2019 at 03:33:20PM +0100, Dr. David Alan Gilbert (git) wrote: > > > > +static void vuf_device_realize(DeviceState *dev, Error **errp) > > > > +{ > > > > + VirtIODevice *vdev = VIRTIO_DEVICE(dev); > > > > + VHostUserFS *fs = VHOST_USER_FS(dev); > > > > + unsigned int i; > > > > + size_t len; > > > > + int ret; > > > > + > > > > + if (!fs->conf.chardev.chr) { > > > > + error_setg(errp, "missing chardev"); > > > > + return; > > > > + } > > > > + > > > > + if (!fs->conf.tag) { > > > > + error_setg(errp, "missing tag property"); > > > > + return; > > > > + } > > > > + len = strlen(fs->conf.tag); > > > > + if (len == 0) { > > > > + error_setg(errp, "tag property cannot be empty"); > > > > + return; > > > > + } > > > > + if (len > sizeof_field(struct virtio_fs_config, tag)) { > > > > + error_setg(errp, "tag property must be %zu bytes or less", > > > > + sizeof_field(struct virtio_fs_config, tag)); > > > > + return; > > > > + } > > > > + > > > > + if (fs->conf.num_queues == 0) { > > > > + error_setg(errp, "num-queues property must be larger than 0"); > > > > + return; > > > > + } > > > > > > The strange thing is that actual # of queues is this number + 2. > > > And this affects an optimal number of vectors (see patch 2). > > > Not sure what a good solution is - include the > > > mandatory queues in the number? > > > Needs to be documented in some way. > > > > Should we be doing nvectors the same way virtio-scsi-pci does it; > > with a magic 'unspecified' default where it sets the nvectors based on > > the number of queues? > > > > I think my preference is not to show the users the mandatory queues. > > I agree. Users want to control multiqueue, not on the absolute number > of virtqueues including mandatory queues. I agree as well, but let me advocate again for renaming this to 'num_request_queues' or similar to make it more obvious what this number actually means. > > > > > + > > > > + if (!is_power_of_2(fs->conf.queue_size)) { > > > > + error_setg(errp, "queue-size property must be a power of 2"); > > > > + return; > > > > + } > > > > > > Hmm packed ring allows non power of 2 ... > > > We need to look into a generic helper to support VQ > > > size checks. > > > > Which would also have to include the negotiation of where it's doing > > packaged ring? > > It's impossible to perform this check at .realize() time since the > packed virtqueue layout is negotiated via a VIRTIO feature bit. This > puts us in the awkward position of either failing when the guest has > already booted or rounding up the queue size for split ring layouts > (with a warning message?). I fear that is always going to be awkward if you allow to specify the queue size via a property. Basically, you can do two things: fail to accept FEATURES_OK if the queue size is not a power of 2 and the guest did not negotiate packed ring, or disallow to set a non power of 2 value here, which is what the other devices with such a property currently do (see also my other mail.) Would probably be good if all devices used the same approach (when we introduced packed ring support.)