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 8E5CD16C87B for ; Mon, 22 Jul 2024 11:10:30 +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=1721646632; cv=none; b=kkSep1FfX/tK+CFpTKt6x0DGYd6qbNI0DbeHK1+aNJaq2g9aUxfW23n3Y6ocMMoLyl3c34ROarwA0XLOHBt0cOi4bZu4mTsIeQgLijawk/XxGqqwobMqQMD9YszTmpW1dPFw47a1bmlbby8la1CNYVasX4bBCWHodE04DDpy6+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721646632; c=relaxed/simple; bh=oMAMO7sUOdgfshyC1TIa2Qwn/3USkETxBIrUqUtpAYw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=o5KQXzvfXuOyY2NNWIEdeVEVDGc5+xWK3f4MskTvPV+rsiRhAEtoUkbxkEAmDRjP8wrvkP/PdifucO7wo9i811iWdl4eKlkKNHTJo+v1HX7U4ic7pJGpiuJhwZebIJGmkiFvIyZx7aFaC4ONkaft4XEvPAO5njqlzqWgZpsgBUY= 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=CbZzMVLW; 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="CbZzMVLW" Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 606E52B3; Mon, 22 Jul 2024 13:09:41 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1721646581; bh=oMAMO7sUOdgfshyC1TIa2Qwn/3USkETxBIrUqUtpAYw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CbZzMVLWkHzFV74YUZ4oHY+TeGQPt3u4JS2mp5UT/5pj5ppEZEyWik6S6YFlkZTQU nAldbNDVyDPGpyirdejQG9HuSW+EzcUCWzvYhQPnpGX4kRecUWKQ7XqVqv64J1dPdW /hZH+5Z9Pb+tFZ+i3oqV6Vg1VO+6ut24rRF98Wxw= Date: Mon, 22 Jul 2024 14:10:04 +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: <20240722111004.GB13497@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> 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: <20240722104407.GB4252@unreal> Hi Leon, 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 subsystem. 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