From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [213.167.242.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A57571DFE3 for ; Mon, 22 Jul 2024 14:14:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.167.242.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721657645; cv=none; b=DOLvOdbA7qNQ0izbqxdktAd9bu5YTAHr25IUmEL41dQVsaQ+QGOevFAbSwm5MtixWWkxJiKaf5gjnRROJuDSEPIMAv0qOzJ/xKux+xmcBfWl91QHnjEF7IpSI2t3e4oXj2DVhd2t0biFVTj6OsLw3Tg4imCh6CBltFq2uqyLa2I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721657645; c=relaxed/simple; bh=7krbkr0FK8DqcuZDb5Bm0pBNAW/DS8NOrsIa/1qGT+c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NL2RJbJWgTdzq8LM4EixaE5H0JJRRGjOgigNu9mrYawzQIoV+Ac//i7nhiABj8Xqzs/+rQA54yav5Qet/h0R/huvAu5lOxU7M6V4LUFMcs6j6Fy6iAoidMih/OucUj45u+3UBZBamZLLSv3JsLBi0oa651qoAeQklhA7x/UD/W8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com; spf=pass smtp.mailfrom=ideasonboard.com; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b=HK6/JUGa; arc=none smtp.client-ip=213.167.242.64 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ideasonboard.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="HK6/JUGa" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 68FF3D1F; Mon, 22 Jul 2024 16:13:20 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1721657600; bh=7krbkr0FK8DqcuZDb5Bm0pBNAW/DS8NOrsIa/1qGT+c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HK6/JUGazSPW7upEvsYTHZhQUSWwvNFkDBX+3IsRB1/gy4hqxo/SDQa898JFCSfZT Dg3f17L3sl0qgz+2iOBHdlP04w1KFUzHcd4S5YdHcE1w0EHyLldd6ABbUKgoNEbxUZ OQYsZe+sG0i0V+YIHk085N3ZYnyNWLiGEMYzdHMU= Date: Mon, 22 Jul 2024 17:13:43 +0300 From: Laurent Pinchart To: Leon Romanovsky Cc: Dan Williams , James Bottomley , ksummit@lists.linux.dev, linux-cxl@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, jgg@nvidia.com Subject: Re: [MAINTAINERS SUMMIT] Device Passthrough Considered Harmful? Message-ID: <20240722141343.GH13497@pendragon.ideasonboard.com> References: <668c67a324609_ed99294c0@dwillia2-xfh.jf.intel.com.notmuch> <3b9631cf12f451fc08f410255ebbba23081ada7c.camel@HansenPartnership.com> <668db67196ca3_1bc8329416@dwillia2-xfh.jf.intel.com.notmuch> <20240721192530.GD23783@pendragon.ideasonboard.com> <20240722073119.GA4252@unreal> <20240722085317.GA31279@pendragon.ideasonboard.com> <20240722104407.GB4252@unreal> <20240722111004.GB13497@pendragon.ideasonboard.com> <20240722132828.GC4252@unreal> Precedence: bulk X-Mailing-List: ksummit@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240722132828.GC4252@unreal> On Mon, Jul 22, 2024 at 04:28:28PM +0300, Leon Romanovsky wrote: > On Mon, Jul 22, 2024 at 02:10:04PM +0300, Laurent Pinchart wrote: > > On Mon, Jul 22, 2024 at 01:44:07PM +0300, Leon Romanovsky wrote: > > > On Mon, Jul 22, 2024 at 11:53:17AM +0300, Laurent Pinchart wrote: > > > > On Mon, Jul 22, 2024 at 10:31:19AM +0300, Leon Romanovsky wrote: > > > > > On Sun, Jul 21, 2024 at 10:25:30PM +0300, Laurent Pinchart wrote: > > > > > > On Tue, Jul 09, 2024 at 03:15:13PM -0700, Dan Williams wrote: > > > > > > > James Bottomley wrote: > > > > > > > > > The upstream discussion has yielded the full spectrum of positions on > > > > > > > > > device specific functionality, and it is a topic that needs cross- > > > > > > > > > kernel consensus as hardware increasingly spans cross-subsystem > > > > > > > > > concerns. Please consider it for a Maintainers Summit discussion. > > > > > > > > > > > > > > > > I'm with Greg on this ... can you point to some of the contrary > > > > > > > > positions? > > > > > > > > > > > > > > This thread has that discussion: > > > > > > > > > > > > > > http://lore.kernel.org/0-v1-9912f1a11620+2a-fwctl_jgg@nvidia.com > > > > > > > > > > > > > > I do not want to speak for others on the saliency of their points, all I > > > > > > > can say is that the contrary positions have so far not moved me to drop > > > > > > > consideration of fwctl for CXL. > > > > > > > > > > > > > > Where CXL has a Command Effects Log that is a reasonable protocol for > > > > > > > making decisions about opaque command codes, and that CXL already has a > > > > > > > few years of experience with the commands that *do* need a Linux-command > > > > > > > wrapper. > > > > > > > > > > > > > > Some open questions from that thread are: what does it mean for the fate > > > > > > > of a proposal if one subsystem Acks the ABI and another Naks it for a > > > > > > > device that crosses subsystem functionality? Would a cynical hardware > > > > > > > response just lead to plumbing an NVME admin queue, or CXL mailbox to > > > > > > > get device-specific commands past another subsystem's objection? > > > > > > > > > > > > My default answer would be to trust the maintainers of the relevant > > > > > > subsystems (or try to convince them when you disagree :-)). > > > > > > > > > > You know, trust is a two-way street. If you want to trust maintainers, > > > > > they need to trust others as well. The situation where one maintainer > > > > > says "I don't trust you, so I will not allow you and other X maintainers > > > > > to do Y" is not a healthy situation. > > > > > > > > > > > Not only should they know the technical implications best, they should also have > > > > > > a good view of the whole vertical stack, and the implications of > > > > > > pass-through for their ecosystem. > > > > > > > > > > It is wishful thinking. It is clearly not true for large subsystems > > > > > and/or complex devices. > > > > > > > > Are you saying that kernel communities behind large subsystems for > > > > complex devices generally have no idea about what they're doing ? Or > > > > that in a small number of particular cases those communities are > > > > clueless ? Or does that apply to just the maintainer, not the whole > > > > subsystem core developers ? I'd like to better understand the scale of > > > > your claim here. > > > > > > I don't know how you jumped from saying "the maintainers of the relevant > > > subsystems" to "kernel communities". I'm talking about maintainers, not > > > communities. > > > > I wasn't too sure, so that's why I asked. I have also not been very > > precise in my previous e-mails. When I mentioned trusting maintainers, I > > meant trusting the combined knowledge of the relevant maintainer(s) and > > core developer(s) for a subsystema > > Unfortunately, the reason for this topic proposed for Maintainer's summit > is that the maintainer and core developers are disagree and there is no way > to resolve it, because it is not technical difference, but a philosophical one. Having been involved in a similar disagreement, I'm not sure "philosophical" is the right term. I can't talk about the fwctl issue in particular as I have only vaguely followed the saga, and I will therefore not take a side there, but in general I tend to use "political" instead of "philosophical". The issues of market control, competition and vendor lock-in vs. empowerment also play important roles. This makes it even more difficult to discuss the disagreements openly. > > The number of people that this covers, and how they collectively reach > > agreements, very much depends on subsystems. > > > > > There is no way to know everything about everything. In large subsystems, > > > the stack above kernel is so vast, which makes it impossible to know all > > > use cases. This is why some words (... good ... whole ...) in your sentence > > > are not accurate. > > > > > > So the idea that one maintainer somehow equal to the whole community and > > > this person can block something for other members of the larger community > > > is overreaching. -- Regards, Laurent Pinchart