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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 97476C433EF for ; Thu, 9 Jun 2022 16:06:03 +0000 (UTC) Received: from localhost ([::1]:57730 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nzKfa-0005FI-H7 for qemu-devel@archiver.kernel.org; Thu, 09 Jun 2022 12:06:02 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34032) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzKSD-0008PZ-7f for qemu-devel@nongnu.org; Thu, 09 Jun 2022 11:52:13 -0400 Received: from ssh.movementarian.org ([139.162.205.133]:34150 helo=movementarian.org) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nzKSB-0005Zb-Gz for qemu-devel@nongnu.org; Thu, 09 Jun 2022 11:52:12 -0400 Received: from movement by movementarian.org with local (Exim 4.94.2) (envelope-from ) id 1nzKS2-005dec-Jx; Thu, 09 Jun 2022 16:52:02 +0100 Date: Thu, 9 Jun 2022 16:52:02 +0100 From: John Levon To: Keith Busch Cc: Klaus Jensen , Jinhao Fan , qemu-devel@nongnu.org Subject: Re: [PATCH 1/2] hw/nvme: Implement shadow doorbell buffer support Message-ID: References: <20220608013659.472500-1-fanjinhao21s@ict.ac.cn> <20220608013659.472500-2-fanjinhao21s@ict.ac.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Url: http://www.movementarian.org/ Received-SPF: pass client-ip=139.162.205.133; envelope-from=movement@movementarian.org; helo=movementarian.org X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jun 09, 2022 at 08:29:30AM -0600, Keith Busch wrote: > On Wed, Jun 08, 2022 at 10:55:30PM +0200, Klaus Jensen wrote: > > > > Keith, is this a bug in the kernel? If the code here would expect the > > doorbell buffer to be updated for the admin queue as well, would we > > break? > > The admin queue has to be created before db buffer can be set up, so we can't > rely on it. And this is a performance feature. Admin commands have never been > considered performant, so we decided not to consider it though the spec allows > it. It's not just unnecessary, but enabling shadow doorbells on admin queues will actively break device implementations (such as SPDK), which have had to presume that driver implementations don't use shadow doorbells for the admin queue. regards john