From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757180AbdCUJ0Z (ORCPT ); Tue, 21 Mar 2017 05:26:25 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:47765 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756389AbdCUJ0X (ORCPT ); Tue, 21 Mar 2017 05:26:23 -0400 Date: Tue, 21 Mar 2017 20:25:18 +1100 From: Gavin Shan To: Alex Williamson Cc: Gavin Shan , Bodong Wang , bhelgaas@google.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, saeedm@mellanox.com, Eli Cohen Subject: Re: [PATCH] pci/sriov: Add an option to probe VFs or not before enabling SR-IOV Reply-To: Gavin Shan References: <1490022874-54718-1-git-send-email-bodong@mellanox.com> <20170320230706.GA12252@gwshan> <7bfcfdcd-e0a8-f1e9-f112-fa35fdb845d7@mellanox.com> <20170320225708.6868676a@t450s.home> <20170321054305.GA12230@gwshan> <20170321000158.444991a3@t450s.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170321000158.444991a3@t450s.home> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-MML: disable x-cbid: 17032109-0008-0000-0000-00000119E000 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17032109-0009-0000-0000-00000944CE5D Message-Id: <20170321092518.GA19657@gwshan> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-03-21_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703210084 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 21, 2017 at 12:01:58AM -0600, Alex Williamson wrote: >On Tue, 21 Mar 2017 16:43:05 +1100 >Gavin Shan wrote: >> On Mon, Mar 20, 2017 at 10:57:08PM -0600, Alex Williamson wrote: >> >On Mon, 20 Mar 2017 18:34:23 -0500 >> >Bodong Wang wrote: >> >> .../... >> >> >> > Bodong, I'm not sure if there is a requirement to load driver for the >> >> > specified number of VFs? That indicates no driver will be loaded for >> >> > other VFs. If so, this interface might serve the purpose as well. >> >> Gavin, thanks for the review. That is indeed an interesting suggestion. >> >> Theoretically, we can change that probe_vfs from boolean to integer. >> >> And use it as a counter to probe the first N VFs(if N < total_vfs). >> >> Let's see if there are any objections. >> > >> >Is it just me or does this seem like a confusing user interface, ie. to >> >get binary on/off behavior a user now needs to 'cat total_vfs > >> >sriov_probe_vfs'. It's not very intuitive, what's the use case for it? >> > >> >> After it's changed to integer, it accepts number. If users want to load >> driver for all VFs and don't want to check the maximal number of VFs, >> they can simply write 0xffffffff. So "on" and "off" are replaced with 0xffffffff >> and 0, but users has to press the keyboard more times though. >> >> drivers/net/ethernet/mellanox/mlx4/main.c::probe_vfs_argc allows to specify >> the number of VFs with which we're going to bind drivers. Less time is needed >> to enable SRIOV capability. As I had in some development environment: assume >> PF supports 256 VFs and I'm going to enable all of them, but I only want to >> load driver for two of them, then test the data path on those two VFs. Besides, >> I can image the VF needn't a driver in host if it's going to be passed to guest. >> Not sure how much sense it makes. > >Yes, I understand what you're trying to do, but I still think it's >confusing for a user interface. This also doesn't answer what's the >practical, typical user case you see where it's useful to probe some >VFs but not others. The case listed is a development case where you >could just as easily disable all probing, then manually bind the first >two VFs to the host driver. Which is the better design, impose a >confusing interface on all users to simplify an obscure development >environment or simplify the user interface and assume developers know >how to bind devices otherwise? Thanks, > Yeah, your explanation is also fairly reasonable. The interface has been named as "probe_vfs" instead of "probe_vf" or "probe_vf_driver". So it seems it should accept number of VFs on which drivers are loaded. Besides, making this interface accept number corresponds to 3 possiblities: all, none and load drivers on part of available VFs. So more flexibility is gained. User can theoritically have the use case as I had - passing through some of the VFs to guest: (A) All VFs are bound with drivers; (B) unbind the drivers for some of the VFs; (C) bind the VFs with vfio-pci; (D) passing through; (A) is overhead in this scenario. Some CPU cycles are saved if (A) is avoided. Thanks, Gavin