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,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 CA20BC43215 for ; Wed, 27 Nov 2019 10:59:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 987F1206BF for ; Wed, 27 Nov 2019 10:59:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RMbs3T33" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726510AbfK0K7R (ORCPT ); Wed, 27 Nov 2019 05:59:17 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:23537 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726267AbfK0K7R (ORCPT ); Wed, 27 Nov 2019 05:59:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574852356; 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=d3vy1tSD+75AOc1W4isJ3oQZhdb0GEOYttsw31Fy3lA=; b=RMbs3T333G/s+w6x8Atqn1Tg0m2DCI7rZi1nxScDjV6EKqSI3fbbqzbQso5iCCVe3pOnhg p63+pwctKLGwKgYqnRgRhWHOame0m6WsIADGdr4Y7MUnvX675O9l58Mn1ogd3xhdxzmX6+ +6a5jg1NggPyofca6yqNj0JcCrWu/6E= 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-260-UcxD0TuwMESSHJcJUhxLxQ-1; Wed, 27 Nov 2019 05:59:13 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7B29A18A8C8B; Wed, 27 Nov 2019 10:59:11 +0000 (UTC) Received: from [10.72.12.78] (ovpn-12-78.pek2.redhat.com [10.72.12.78]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5B8FA608AC; Wed, 27 Nov 2019 10:59:00 +0000 (UTC) Subject: Re: [net-next v2 1/1] virtual-bus: Implementation of Virtual Bus To: Martin Habets , Parav Pandit , Jeff Kirsher , "davem@davemloft.net" , "gregkh@linuxfoundation.org" Cc: Dave Ertman , "netdev@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "nhorman@redhat.com" , "sassmann@redhat.com" , "jgg@ziepe.ca" , Kiran Patil , "Michael S. Tsirkin" , Alex Williamson , "Bie, Tiwei" References: <20191115223355.1277139-1-jeffrey.t.kirsher@intel.com> <30b968cf-0e11-a2c6-5b9f-5518df11dfb7@solarflare.com> <22dd6ae3-03f4-1432-2935-8df5e9a449de@redhat.com> From: Jason Wang Message-ID: <0b845456-54b2-564a-0979-ba55bcf3269c@redhat.com> Date: Wed, 27 Nov 2019 18:58:58 +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: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: UcxD0TuwMESSHJcJUhxLxQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/11/26 =E4=B8=8B=E5=8D=888:26, Martin Habets wrote: > On 22/11/2019 16:19, Parav Pandit wrote: >> >>> From: Jason Wang >>> Sent: Friday, November 22, 2019 3:14 AM >>> >>> On 2019/11/21 =E4=B8=8B=E5=8D=8811:10, Martin Habets wrote: >>>> On 19/11/2019 04:08, Jason Wang wrote: >>>>> On 2019/11/16 =E4=B8=8A=E5=8D=887:25, Parav Pandit wrote: >>>>>> Hi Jeff, >>>>>> >>>>>>> From: Jeff Kirsher >>>>>>> Sent: Friday, November 15, 2019 4:34 PM >>>>>>> >>>>>>> From: Dave Ertman >>>>>>> >>>>>>> This is the initial implementation of the Virtual Bus, >>>>>>> virtbus_device and virtbus_driver.=C2=A0 The virtual bus is a softw= are >>>>>>> based bus intended to support lightweight devices and drivers and >>>>>>> provide matching between them and probing of the registered drivers= . >>>>>>> >>>>>>> The primary purpose of the virual bus is to provide matching >>>>>>> services and to pass the data pointer contained in the >>>>>>> virtbus_device to the virtbus_driver during its probe call.=C2=A0 T= his >>>>>>> will allow two separate kernel objects to match up and start >>> communication. >>>>>> It is fundamental to know that rdma device created by virtbus_driver= will >>> be anchored to which bus for an non abusive use. >>>>>> virtbus or parent pci bus? >>>>>> I asked this question in v1 version of this patch. >>>>>> >>>>>> Also since it says - 'to support lightweight devices', documenting t= hat >>> information is critical to avoid ambiguity. >>>>>> Since for a while I am working on the subbus/subdev_bus/xbus/mdev [1= ] >>> whatever we want to call it, it overlaps with your comment about 'to su= pport >>> lightweight devices'. >>>>>> Hence let's make things crystal clear weather the purpose is 'only >>> matching service' or also 'lightweight devices'. >>>>>> If this is only matching service, lets please remove lightweight dev= ices >>> part.. >>>>> Yes, if it's matching + lightweight device, its function is almost a = duplication >>> of mdev. And I'm working on extending mdev[1] to be a generic module to >>> support any types of virtual devices a while. The advantage of mdev is: >>>>> 1) ready for the userspace driver (VFIO based) >>>>> 2) have a sysfs/GUID based management interface >>>> In my view this virtual-bus is more generic and more flexible than mde= v. >>> >>> Even after the series [1] here? > I have been following that series. It does make mdev more flexible, and a= lmost turns it into a real bus. > Even with those improvements to mdev the virtual-bus is in my view still = more generic and more flexible, > and hence more future-proof. So the only difference so far is after that series is: 1) mdev has sysfs support 2) mdev has support from vfio For 1) we can decouple that part to be more flexible, for 2) I think you=20 would still need that part other than inventing a new VFIO driver (e.g=20 vfio-virtual-bus)? > >>>> What for you are the advantages of mdev to me are some of it's >>> disadvantages. >>>> The way I see it we can provide rdma support in the driver using virtu= al-bus. >> This is fine, because it is only used for matching service. >> >>> Yes, but since it does matching only, you can do everything you want. >>> But it looks to me Greg does not want a bus to be an API multiplexer. S= o if a >>> dedicated bus is desired, it won't be much of code to have a bus on you= r own. > I did not intend for it to be a multiplexer. And I very much prefer a gen= eric bus over a any driver specific bus. > >> Right. virtbus shouldn't be a multiplexer. >> Otherwise mdev can be improved (abused) exactly the way virtbus might. W= here 'mdev m stands for multiplexer too'. :-) >> No, we shouldn=E2=80=99t do that. >> >> Listening to Greg and Jason G, I agree that virtbus shouldn't be a multi= plexer. >> There are few basic differences between subfunctions and matching servic= e device object. >> Subfunctions over period of time will have several attributes, few that = I think of right away are: >> 1. BAR resource info, write combine info >> 2. irq vectors details >> 3. unique id assigned by user (while virtbus will not assign such user i= d as they are auto created for matching service for PF/VF) >> 4. rdma device created by matched driver resides on pci bus or parent de= vice >> While rdma and netdev created on over subfunctions are linked to their o= wn 'struct device'. > This is more aligned with my thinking as well, although I do not call the= se items subfunctions. > There can be different devices for different users, where multiple can be= active at the same time (with some constraints). > > One important thing to note is that there may not not be a netdev device.= What we traditionally call > a "network driver" will then only manage the virtualised devices. > >> Due to that sysfs view for these two different types of devices is bit d= ifferent. >> Putting both on same bus just doesn't appear right with above fundamenta= l differences of core layer. > Can you explain which code layer you mean? > >>>> At the moment we would need separate mdev support in the driver for >>>> vdpa, but I hope at some point mdev would become a layer on top of vir= tual- >>> bus. >> How is it optimal to create multiple 'struct device' for single purpose? >> Especially when one wants to create hundreds of such devices to begin wi= th. >> User facing tool should be able to select device type and place the devi= ce on right bus. > At this point I think it is not possible to create a solution that is opt= imal right now for all use cases. Probably yes. > With the virtual bus we do have a solid foundation going forward, for the= users we know now and for > future ones. If I understand correctly, if multiplexer is not preferred. It would be=20 hard to have a bus on your own code, there's no much code could be reused. Thanks > Optimisation is something that needs to happen over time, without break= ing existing users. > > As for the user facing tool, the only one I know of that always works is = "echo" into a sysfs file. > > Best regards, > Martin >