From mboxrd@z Thu Jan 1 00:00:00 1970 From: Auger Eric Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs Date: Fri, 16 Apr 2021 16:26:19 +0200 Message-ID: References: <20210401134236.GF1463678@nvidia.com> <20210401160337.GJ1463678@nvidia.com> <4bea6eb9-08ad-4b6b-1e0f-c97ece58a078@redhat.com> <20210415230732.GG1370958@nvidia.com> <20210416140524.GI1370958@nvidia.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618583199; 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=t1Hv2NbQ/MlDR82Y8nOIlqSLTEiVX08oupchgjJ9jRA=; b=O1rjioiI59LvC+S4nBSeMhvzoA5ceS7spb7jFCdkjrRNpFC6fI2SWlI3K6TOtlvalhf1eK N8JyO3WbCICOTkpav9TbWyRS8TN7sLxljNHIGja8vud0uQjveKKbJMfRJFUsKy+0WG39bV fUYD+aLmoTlKKHb4d/5H4oRLVS0daMQ= In-Reply-To: <20210416140524.GI1370958-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii" To: Jason Gunthorpe Cc: "Liu, Yi L" , Jean-Philippe Brucker , "Tian, Kevin" , Jacob Pan , LKML , Joerg Roedel , Lu Baolu , David Woodhouse , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Tejun Heo , Li Zefan , Johannes Weiner , Jean-Philippe Brucker , Alex Williamson , Jonathan Corbet , "Raj, Ashok" , "Wu, Hao" , "Jiang, Dave" Hi, On 4/16/21 4:05 PM, Jason Gunthorpe wrote: > On Fri, Apr 16, 2021 at 03:38:02PM +0200, Auger Eric wrote: > >> The redesign requirement came pretty late in the development process. >> The iommu user API is upstream for a while, the VFIO interfaces have >> been submitted a long time ago and under review for a bunch of time. >> Redesigning everything with a different API, undefined at this point, is >> a major setback for our work and will have a large impact on the >> introduction of features companies are looking forward, hence our >> frustration. > > I will answer both you and Jacob at once. > > This is uAPI, once it is set it can never be changed. > > The kernel process and philosophy is to invest heavily in uAPI > development and review to converge on the best uAPI possible. > > Many past submissions have take a long time to get this right, there > are several high profile uAPI examples. > > Do you think this case is so special, or the concerns so minor, that it > should get to bypass all of the normal process? That's not my intent to bypass any process. I am just trying to understand what needs to be re-designed and for what use case. > > Ask yourself, is anyone advocating for the current direction on > technical merits alone? > > Certainly the patches I last saw where completely disgusting from a > uAPI design perspective. > > It was against the development process to organize this work the way > it was done. Merging a wack of dead code to the kernel to support a > uAPI vision that was never clearly articulated was a big mistake. > > Start from the beginning. Invest heavily in defining a high quality > uAPI. Clearly describe the uAPI to all stake holders. This was largely done during several confs including plumber, KVM forum, for several years. Also API docs were shared on the ML. I don't remember any voice was raised at those moments. Break up the > implementation into patch series without dead code. Make the > patches. Remove the dead code this group has already added. > > None of this should be a surprise. The VDPA discussion and related > "what is a mdev" over a year ago made it pretty clear VFIO is not the > exclusive user of "IOMMU in userspace" and that places limits on what > kind of uAPIs expansion it should experience going forward. Maybe clear for you but most probably not for many other stakeholders. Anyway I do not intend to further argue and I will be happy to learn from you and work with you, Jacob, Liu and all other stakeholders to define a better integration. Thanks Eric > > Jason >