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=-2.3 required=3.0 tests=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 E099CC742B0 for ; Fri, 12 Jul 2019 09:20:27 +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 B964421670 for ; Fri, 12 Jul 2019 09:20:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B964421670 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:47710 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlrj8-0006BF-7M for qemu-devel@archiver.kernel.org; Fri, 12 Jul 2019 05:20:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41150) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlriw-0005en-FZ for qemu-devel@nongnu.org; Fri, 12 Jul 2019 05:20:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hlriv-0005G6-Cq for qemu-devel@nongnu.org; Fri, 12 Jul 2019 05:20:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37586) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hlrit-0005CW-1W; Fri, 12 Jul 2019 05:20:11 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 84CC185543; Fri, 12 Jul 2019 09:20:09 +0000 (UTC) Received: from dhcp-200-226.str.redhat.com (dhcp-200-226.str.redhat.com [10.33.200.226]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1E7CC19C58; Fri, 12 Jul 2019 09:20:07 +0000 (UTC) Date: Fri, 12 Jul 2019 11:20:06 +0200 From: Kevin Wolf To: Maxim Levitsky Message-ID: <20190712092006.GA4514@dhcp-200-226.str.redhat.com> References: <20190704124342.7753-1-mlevitsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190704124342.7753-1-mlevitsk@redhat.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Fri, 12 Jul 2019 09:20:09 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 0/1] Don't obey the kernel block device max transfer len / max segments for raw block devices 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: Fam Zheng , John Ferlan , qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 04.07.2019 um 14:43 hat Maxim Levitsky geschrieben: > Linux block devices, even in O_DIRECT mode don't have any user visible > limit on transfer size / number of segments, which underlying kernel block device can have. > The kernel block layer takes care of enforcing these limits by splitting the bios. > > By limiting the transfer sizes, we force qemu to do the splitting itself which > introduces various overheads. > It is especially visible in nbd server, where the low max transfer size of the > underlying device forces us to advertise this over NBD, thus increasing the > traffic overhead in case of image conversion which benefits from large blocks. > > More information can be found here: > https://bugzilla.redhat.com/show_bug.cgi?id=1647104 > > Tested this with qemu-img convert over nbd and natively and to my surprise, > even native IO performance improved a bit. Thanks, applied to the block branch. Kevin