From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49266) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vky1O-0000l3-Ts for qemu-devel@nongnu.org; Mon, 25 Nov 2013 10:24:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Vky1G-0007k8-Go for qemu-devel@nongnu.org; Mon, 25 Nov 2013 10:24:22 -0500 Received: from mx.ipv6.kamp.de ([2a02:248:0:51::16]:51084 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Vky1G-0007jl-4p for qemu-devel@nongnu.org; Mon, 25 Nov 2013 10:24:14 -0500 Message-ID: <52936BB0.1020608@kamp.de> Date: Mon, 25 Nov 2013 16:24:32 +0100 From: Peter Lieven MIME-Version: 1.0 References: <1385387840-17307-1-git-send-email-pl@kamp.de> <1385387840-17307-4-git-send-email-pl@kamp.de> <529364B5.6000202@redhat.com> <529367C8.7080301@kamp.de> <52936951.3090602@redhat.com> In-Reply-To: <52936951.3090602@redhat.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: kwolf@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com On 25.11.2013 16:14, Paolo Bonzini wrote: > Il 25/11/2013 16:07, Peter Lieven ha scritto: >>>> since the convert process is basically a sync operation it might >>>> be benificial in some case to change the hardcoded I/O buffer >>>> size to an alternate (greater) value. >>> Do you really need the extra knob? You can just add to BlockLimits the >>> optimal transfer length, and use it unconditionally. >> If you say patch 5 and 3 are ok. What could be done is to remove >> this knob and increase the iobuf_size to cluster_size if cluster_size >> is greater. > Yes, that makes sense because it avoids unnecessary COW. > >> I do not want to increase the default iobuf size to anything >> greater than 2MB. I do not know why this was choosen, but maybe >> there was a reason for it. > I think it is fine to increase it to the cluster_size or even to the > optimal transfer length (new BlockLimits field). okay scsi speaking: bs->bl.optimal_transfer_length = max(iscsilun->bl.opt_xfer_len, iscsilun->bl.opt_unmap_gran) ? bdi->cluster_size as in Patch 3? > >> The storages we use here have a very strange page size of 15MB. >> If I sent aligned 15MB chunks the performace is about +50% compared >> to the original qemu-img. > I think composing the optimal transfer length and optimal unmap > granularity (cluster_size) will work well: > > * clamp maximum size to optimal transfer length. or increase it if its larger. for the dell equallogic storages we use the opt_unmap_gran is 15MB!!! > > * then, round final sector down to unmap granularity okay, i will try your modification to only round down the last sector. would you use bdi->cluster_size or the unmap alignment field from the bs->bl? Peter