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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BEDF7C83F27 for ; Mon, 21 Jul 2025 06:26:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Ehy6hUp1kz0pFsTwkR8JoJ2x3t/8iTZNHHHKGUSHiE8=; b=NxOUjYzd/zVv+pcNbbrDBMx4Nq WabYRXjFLSNqviwdVG2XrYZqBTiDfcD952EfJi+n3KboI4Ur7LIHQNIuzkowX9L0cTRTIOXLTlHlF 0owbDrTjjyWXtz7fmL8zhxt9hGtzG9ZfI5QqcNU7FGJWc729rdb4p5zVAAyRN83KB0dFtordlNgLv YkEKbYG95gfrc2HgMkiOcYXSLmm0UMpBhB/3y5mGKqSkSIzN5KfK8ZK1MZEKEdbZjhRVAIFDXiSmc suWiQM2ND8Zc9tNg35rnw2p15nna8iRlWVd30BGLBDdqJ0feaUoq2Ct8977/eGmh3qpY9jWuwR8io 2LKJrRBA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1udjye-0000000GMZB-3eh3; Mon, 21 Jul 2025 06:26:20 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1udjyc-0000000GMWb-2pCi for linux-nvme@lists.infradead.org; Mon, 21 Jul 2025 06:26:20 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 7425B68AFE; Mon, 21 Jul 2025 08:26:00 +0200 (CEST) Date: Mon, 21 Jul 2025 08:26:00 +0200 From: Christoph Hellwig To: Joel Granados Cc: Christoph Hellwig , Keith Busch , Jens Axboe , Sagi Grimberg , Klaus Jensen , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 0/8] nvme: Add Controller Data Queue to the nvme driver Message-ID: <20250721062600.GA28867@lst.de> References: <20250714-jag-cdq-v1-0-01e027d256d5@kernel.org> <20250714130230.GA7752@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250720_232618_853654_29054795 X-CRM114-Status: GOOD ( 22.90 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Fri, Jul 18, 2025 at 01:33:34PM +0200, Joel Granados wrote: > > to win a point. So for CDQs to be useful in Linux we'll need the > > proper live migration still under heavy development. With that I'd > Do you mean in the specification body or patch series in the mailing > lists? Actual code. As I said I very much expect CDQ creation and usage to be kernel driven for live migration. > > very much expect the kernel to manage the CDQs just like any other > > queue, and not a random user ioctl. > This is a great segue to a question: If CDQ is like any other queue, > what is the best way of handling the lack of CDQ submission queues? > Something like snooping all submissions for these CDQs and triggering a > CDQ consume on every submission? I don't understand this question and proposed answer at all all. > I went with the ioctl as the faster way to get it to work; Get _what_ to work? > I might > explore what having it as just another queue would look like. > > > So what would be the use case for a user controlled CDQ? > Do you mean a hypothetical list besides LM in NVME 2.2? As out line in the last two mails I don't see how live migration would work with user controlled CDQs. Maybe I'm wrong, but nothing in this thread seems to even try to explain how that would work.