From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 49B712AD04 for ; Mon, 21 Jul 2025 06:26:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753079167; cv=none; b=uRmMQpUnV6yYaMi0RPNn33z201QjCv7623WYebfDAFqNFYou5HoyCVLtQETXmsE9enCLOTeI/6Kuokitt4XHSU+IU0isls0KTh7N1d+5QO6eECNiEX5Fcp0Y7PGzV0J75FB+oc1TmEw+X1sozPvwNYB7CXeYqMKZBn5+3pP7vUU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753079167; c=relaxed/simple; bh=AwpLY7EbWsOdpzEv1EsGSeym2rHI8iqPutv6BppbmAo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Jt9fXs6H09j4mYdD+ttA5ZYDpnNhof35sCBtUjvFQLw2uvQs8YgzMPBnlBnvic1p/+Wb25/Uyh00XW9rXaxmh37lE+JqJ5r5zqYRMLjLuY1opqy+3pUB0WCBB0IqqiTN36rnSqSPByTdq08BcmbyAt1VMsBftE+NqLdDgGEa0oA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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) 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.