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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 EBD53C3A5A2 for ; Fri, 23 Aug 2019 19:02:08 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id B75E821848 for ; Fri, 23 Aug 2019 19:02:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=grep.be header.i=@grep.be header.b="eRyW0p+n" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B75E821848 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=uter.be Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:32994 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i1Ep5-0001pj-0z for qemu-devel@archiver.kernel.org; Fri, 23 Aug 2019 15:02:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42081) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i1EcG-0005KW-Al for qemu-devel@nongnu.org; Fri, 23 Aug 2019 14:48:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i1EcF-0007jQ-5T for qemu-devel@nongnu.org; Fri, 23 Aug 2019 14:48:52 -0400 Received: from latin.grep.be ([2a01:4f8:140:52e5::2]:56902) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i1EcB-0007cf-PW; Fri, 23 Aug 2019 14:48:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=grep.be; s=2017.latin; h=Sender: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-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=e7wsTJl6QOI6Q9EVw8/xuD/OXkt0OO7+/npHSalZAOk=; b=eRyW0p+n3tRTBjYatAmew90oW5 L96WaLsHDyHrYcsbyL/XiS42jANqpZ1YYrkqr+X1fdZ6lcqYLiLtp0O/QqBbZWp5FpsbfmRKa+Gsn q0ogvdpjphgUzx7yVcNuc2NOIoro/pnCvBSpgC8bBK9/OB3ZrZr6ulOd03OAQcTweSvsxvSPPUWGV 320ptQcOFUmtlgoz+DsCFtULa7KU7aKXdDeMj32W44+LfVFIgesz6Waa/sqI7t1YwgEyLHG81Xq29 ZvBEfBmgpu8e8cR6uzUSx26ynBKMeivpsFeurFarmRriyCaYCGktsA6NbfoepFW/JKq4sD7dGLPiT KjcJVkXw==; Received: from wouter by latin.grep.be with local (Exim 4.89) (envelope-from ) id 1i1Eby-0003hv-Q2; Fri, 23 Aug 2019 20:48:34 +0200 Date: Fri, 23 Aug 2019 20:48:34 +0200 From: Wouter Verhelst To: Eric Blake Message-ID: <20190823184834.brhsfbc4sdq5xuij@grep.be> References: <25ead363-4f37-5450-b985-1876374e314d@redhat.com> <20190823143426.26838-1-eblake@redhat.com> <20190823143426.26838-2-eblake@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190823143426.26838-2-eblake@redhat.com> X-Speed: Gates' Law: Every 18 months, the speed of software halves. User-Agent: NeoMutt/20170113 (1.7.2) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2a01:4f8:140:52e5::2 Subject: Re: [Qemu-devel] [PATCH 1/1] protocol: Add NBD_CMD_FLAG_FAST_ZERO X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: libguestfs@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org, nbd@other.debian.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Aug 23, 2019 at 09:34:26AM -0500, Eric Blake wrote: > +- bit 4, `NBD_CMD_FLAG_FAST_ZERO`; valid during > + `NBD_CMD_WRITE_ZEROES`. If set, but the server cannot perform the > + write zeroes any faster than it would for an equivalent > + `NBD_CMD_WRITE`, One way of fulfilling the letter of this requirement but not its spirit could be to have background writes; that is, the server makes a note that the zeroed region should contain zeroes, makes an error-free reply to the client, and then starts updating things in the background (with proper layering so that an NBD_CMD_READ would see zeroes). This could negatively impact performance after that command to the effect that syncing the device would be slower rather than faster, if not done right. Do we want to keep that in consideration? -- Home is where you have to wash the dishes. -- #debian-devel, Freenode, 2004-09-22