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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 652BFC433E9 for ; Wed, 17 Feb 2021 18:03:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A14664E5B for ; Wed, 17 Feb 2021 18:03:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234748AbhBQSDf (ORCPT ); Wed, 17 Feb 2021 13:03:35 -0500 Received: from mail.kernel.org ([198.145.29.99]:39850 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234708AbhBQSD1 (ORCPT ); Wed, 17 Feb 2021 13:03:27 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id E9A1564E28; Wed, 17 Feb 2021 18:02:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613584961; bh=ITx9kpyYGrtDDs+FqbWm9mIa5z882OIHwezCiMY2pNQ=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=ZMn167je5YaTeRaqjcApDljVQ6Ywgh0Mi7QvrMCPEBWPHSqabjwWv3yjJUsHObdPk VkkT+ThgjE3Aw5x5RStbb+oGrVUhdoWEB8vEfph42WnYXAblb0i68M28P9y6JydeN1 0E1uK39eZLWISx25+FndvAm5fQTtKv2VuKX2UfDr0FU1jjoGWSTDcfojVvvHACweRX pigRybcFSb85JsOBT0RijPPnIpnyvS1dJd9+cxMpBvv0QAzKDgFM8DJyWNs0Thj3+T EMP2A5cRJ/NEtN6a6ED15+0Ucn3A+H2qUr5E7FYA2RsTKwUsw3DC+/VbtmHZ1cb/Or Ubqif6IS/2mVA== Date: Wed, 17 Feb 2021 12:02:39 -0600 From: Bjorn Helgaas To: Leon Romanovsky Cc: Bjorn Helgaas , Saeed Mahameed , Jason Gunthorpe , Alexander Duyck , Jakub Kicinski , linux-pci@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, Don Dutile , Alex Williamson , "David S . Miller" , Greg Kroah-Hartman , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= Subject: Re: [PATCH mlx5-next v6 1/4] PCI: Add sysfs callback to allow MSI-X table size change of SR-IOV VFs Message-ID: <20210217180239.GA896669@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org [+cc Greg in case he wants to chime in on the sysfs discussion. TL;DR: we're trying to add/remove sysfs files when a PCI driver that supports certain callbacks binds or unbinds; series at https://lore.kernel.org/r/20210209133445.700225-1-leon@kernel.org] On Tue, Feb 16, 2021 at 09:58:25PM +0200, Leon Romanovsky wrote: > On Tue, Feb 16, 2021 at 10:12:12AM -0600, Bjorn Helgaas wrote: > > On Tue, Feb 16, 2021 at 09:33:44AM +0200, Leon Romanovsky wrote: > > > On Mon, Feb 15, 2021 at 03:01:06PM -0600, Bjorn Helgaas wrote: > > > > On Tue, Feb 09, 2021 at 03:34:42PM +0200, Leon Romanovsky wrote: > > > > > From: Leon Romanovsky > > > > > +int pci_enable_vf_overlay(struct pci_dev *dev) > > > > > +{ > > > > > + struct pci_dev *virtfn; > > > > > + int id, ret; > > > > > + > > > > > + if (!dev->is_physfn || !dev->sriov->num_VFs) > > > > > + return 0; > > > > > + > > > > > + ret = sysfs_create_files(&dev->dev.kobj, sriov_pf_dev_attrs); > > > > > > > > But I still don't like the fact that we're calling > > > > sysfs_create_files() and sysfs_remove_files() directly. It makes > > > > complication and opportunities for errors. > > > > > > It is not different from any other code that we have in the kernel. > > > > It *is* different. There is a general rule that drivers should not > > call sysfs_* [1]. The PCI core is arguably not a "driver," but it is > > still true that callers of sysfs_create_files() are very special, and > > I'd prefer not to add another one. > > PCI for me is a bus, and bus is the right place to manage sysfs. > But it doesn't matter, we understand each other positions. > > > > Let's be concrete, can you point to the errors in this code that I > > > should fix? > > > > I'm not saying there are current errors; I'm saying the additional > > code makes errors possible in future code. For example, we hope that > > other drivers can use these sysfs interfaces, and it's possible they > > may not call pci_enable_vf_overlay() or pci_disable_vfs_overlay() > > correctly. > > If not, we will fix, we just need is to ensure that sysfs name won't > change, everything else is easy to change. > > > Or there may be races in device addition/removal. We have current > > issues in this area, e.g., [2], and they're fairly subtle. I'm not > > saying your patches have these issues; only that extra code makes more > > chances for mistakes and it's more work to validate it. > > > > > > I don't see the advantage of creating these files only when > > > > the PF driver supports this. The management tools have to > > > > deal with sriov_vf_total_msix == 0 and sriov_vf_msix_count == > > > > 0 anyway. Having the sysfs files not be present at all might > > > > be slightly prettier to the person running "ls", but I'm not > > > > sure the code complication is worth that. > > > > > > It is more than "ls", right now sriov_numvfs is visible without > > > relation to the driver, even if driver doesn't implement > > > ".sriov_configure", which IMHO bad. We didn't want to repeat. > > > > > > Right now, we have many devices that supports SR-IOV, but small > > > amount of them are capable to rewrite their VF MSI-X table siz. > > > We don't want "to punish" and clatter their sysfs. > > > > I agree, it's clutter, but at least it's just cosmetic clutter > > (but I'm willing to hear discussion about why it's more than > > cosmetic; see below). > > It is more than cosmetic and IMHO it is related to the driver role. > This feature is advertised, managed and configured by PF. It is very > natural request that the PF will view/hide those sysfs files. Agreed, it's natural if the PF driver adds/removes those files. But I don't think it's *essential*, and they *could* be static because of this: > > From the management software point of view, I don't think it matters. > > That software already needs to deal with files that don't exist (on > > old kernels) and files that contain zero (feature not supported or no > > vectors are available). I wonder if sysfs_update_group() would let us have our cake and eat it, too? Maybe we could define these files as static attributes and call sysfs_update_group() when the PF driver binds or unbinds? Makes me wonder if the device core could call sysfs_update_group() when binding/unbinding drivers. But there are only a few existing callers, and it looks like none of them are for the bind/unbind situation, so maybe that would be pointless. > > From my point of view, pci_enable_vf_overlay() or > > pci_disable_vfs_overlay() are also clutter, at least compared to > > static sysfs attributes. > > > > > > I see a hint that Alex might have requested this "only visible when PF > > > > driver supports it" functionality, but I don't see that email on > > > > linux-pci, so I missed the background. > > > > > > First version of this patch had static files solution. > > > https://lore.kernel.org/linux-pci/20210103082440.34994-2-leon@kernel.org/#Z30drivers:pci:iov.c > > > > Thanks for the pointer to the patch. Can you point me to the > > discussion about why we should use the "only visible when PF driver > > supports it" model? > > It is hard to pinpoint specific sentence, this discussion is spread > across many emails and I implemented it in v4. > > See this request from Alex: > https://lore.kernel.org/linux-pci/20210114170543.143cce49@omen.home.shazbot.org/ > and this is my acknowledge: > https://lore.kernel.org/linux-pci/20210116082331.GL944463@unreal/ > > BTW, I asked more than once how these sysfs knobs should be handled > in the PCI/core. Thanks for the pointers. This is the first instance I can think of where we want to create PCI core sysfs files based on a driver binding, so there really isn't a precedent. > > [1] https://lore.kernel.org/linux-pci/YBmG7qgIDYIveDfX@kroah.com/ > > [2] https://lore.kernel.org/linux-pci/20200716110423.xtfyb3n6tn5ixedh@pali/