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 X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AAC6C43381 for ; Tue, 22 Dec 2020 14:38:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E780D22510 for ; Tue, 22 Dec 2020 14:38:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727678AbgLVOhw (ORCPT ); Tue, 22 Dec 2020 09:37:52 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:59839 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727653AbgLVOhw (ORCPT ); Tue, 22 Dec 2020 09:37:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608647785; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=VOk6E6hPe7usXLD5bNCDmNIcAC8JFXb+4t0X8eR9cr4=; b=SJrIVV5eVXvMCpxds2FaAP370gHMJTsymQkasmhElVk1sVj0xk9jEYt07EdPohBfgTrugi WoEXSt8aJUhBq+f5U7KQjrsoZuz0MqTcV7yryV/OEnivShpepOIAgDYDhNo2XFmB7WnQuH qkD0OcMtZQCvbiX/JrUKPLdvtgWGie8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-456-6XDxApNmPNKJ09t1PSBSsQ-1; Tue, 22 Dec 2020 09:36:22 -0500 X-MC-Unique: 6XDxApNmPNKJ09t1PSBSsQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B74E910054FF; Tue, 22 Dec 2020 14:36:20 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 24A0D6F977; Tue, 22 Dec 2020 14:36:17 +0000 (UTC) Date: Tue, 22 Dec 2020 09:36:16 -0500 From: Mike Snitzer To: Christoph Hellwig Cc: Palmer Dabbelt , josef@toxicpanda.com, bvanassche@acm.org, corbet@lwn.net, kernel-team@android.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, song@kernel.org, dm-devel@redhat.com, linux-kselftest@vger.kernel.org, shuah@kernel.org, agk@redhat.com, michael.christie@oracle.com Subject: Re: [PATCH v1 0/5] dm: dm-user: New target that proxies BIOs to userspace Message-ID: <20201222143616.GB12885@redhat.com> References: <30d39293-80a4-9ef5-92bb-6b6dec464be3@toxicpanda.com> <20201222133246.GA5099@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201222133246.GA5099@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On Tue, Dec 22 2020 at 8:32am -0500, Christoph Hellwig wrote: > On Mon, Dec 14, 2020 at 07:00:57PM -0800, Palmer Dabbelt wrote: > > I haven't gotten a whole lot of feedback, so I'm inclined to at least have some > > reasonable performance numbers before bothering with a v2. > > FYI, my other main worry beside duplicating nbd is that device mapper > really is a stacked interface that sits on top of other block device. > Turning this into something else that just pipes data to userspace > seems very strange. I agree. Only way I'd be interested is if it somehow tackled enabling much more efficient IO. Earlier discussion in this thread mentioned that zero-copy and low overhead wasn't a priority (because it is hard, etc). But the hard work has already been done with io_uring. If dm-user had a prereq of leaning heavily on io_uring and also enabled IO polling for bio-based then there may be a win to supporting it. But unless lower latency (or some other more significant win) is made possible I just don't care to prop up an unnatural DM bolt-on. Mike