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 75C96C433EF for ; Thu, 24 Mar 2022 06:21:04 +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=RXT+F/Ra9tEyH+GWgw8Y1vf3qfYJJwKpOBJtKxL5UvY=; b=XYXmiAmQ0wQVHb9zfbRU29ktFe Q3TEhbkXlPNp4mm1rkdFKTjlZ5lACQ7LUKV8hi2Bq5kAz2mxFYxnvx0hXd9549x2823QRyUyjLXXW bkKZuVZTboyRQUnFr4lf9p5BmR8Nzleq2dWH2XIW2/SvS7c81E9h3xz90qyu11XUcgsfeClxDM5u6 TJtse7z/0Iq3JqQW0RHNK5ZqBZtHVBZquaHICBGh57VqHYV9b17lskmuEfDUz4oTcfClZwA/VeKoH rtoQ/C8iE1zNmhPbKHXETYFAcoEXhaG1jQaICcpZX0yHEu0GtGlZJHEI//RTPTugSAzaBpMzycVkQ 5e98ZXKQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nXGqC-00FoTh-NV; Thu, 24 Mar 2022 06:21:00 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nXGq9-00FoSQ-Ox for linux-nvme@lists.infradead.org; Thu, 24 Mar 2022 06:20:59 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id E22FC68C4E; Thu, 24 Mar 2022 07:20:53 +0100 (CET) Date: Thu, 24 Mar 2022 07:20:53 +0100 From: Christoph Hellwig To: Sagi Grimberg Cc: Jens Axboe , Kanchan Joshi , Kanchan Joshi , Christoph Hellwig , Keith Busch , Pavel Begunkov , io-uring@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, sbates@raithlin.com, logang@deltatee.com, Pankaj Raghav , Javier =?iso-8859-1?Q?Gonz=E1lez?= , Luis Chamberlain , Adam Manzanares , Anuj Gupta Subject: Re: [PATCH 05/17] nvme: wire-up support for async-passthru on char-device. Message-ID: <20220324062053.GA12519@lst.de> References: <20220308152105.309618-6-joshi.k@samsung.com> <7a123895-1102-4b36-2d6e-1e00e978d03d@grimberg.me> <8f45a761-5ecb-5911-1064-9625a285c93d@grimberg.me> <20220316092153.GA4885@test-zns> <11f9e933-cfc8-2e3b-c815-c49a4b7db4ec@grimberg.me> <3ed01280-5487-7206-a326-0cd110118b65@grimberg.me> <666deb0e-fa10-8a39-c1aa-cf3908b3795c@kernel.dk> <28b53100-9930-92d4-ba3b-f9c5e8773808@grimberg.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <28b53100-9930-92d4-ba3b-f9c5e8773808@grimberg.me> 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-20220323_232057_983182_81EE59EE X-CRM114-Status: GOOD ( 18.96 ) 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 Wed, Mar 16, 2022 at 04:50:53PM +0200, Sagi Grimberg wrote: >>> I know, and that was my original question, no one cares that this >>> interface completely lacks this capability? Maybe it is fine, but >>> it is not a trivial assumption given that this is designed to be more >>> than an interface to send admin/vs commands to the controller... >> >> Most people don't really care about or use multipath, so it's not a >> primary goal. > > This statement is generally correct. However what application would be > interested in speaking raw nvme to a device and gaining performance that > is even higher than the block layer (which is great to begin with)? If passthrough is faster than the block I/O path we're doing someting wrong. At best it should be the same performance. That being said multipathing is an integral part of the nvme driver architecture, and the /dev/ngX devices. If we want to support uring async commands on /dev/ngX it will have to support multipath.