From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35711) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WHFhX-0005Vy-SG for qemu-devel@nongnu.org; Sat, 22 Feb 2014 11:45:24 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WHFhS-0005yq-WF for qemu-devel@nongnu.org; Sat, 22 Feb 2014 11:45:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:24974) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WHFhS-0005tb-Oe for qemu-devel@nongnu.org; Sat, 22 Feb 2014 11:45:14 -0500 Date: Sun, 23 Feb 2014 00:45:12 +0800 From: Fam Zheng Message-ID: <20140222164512.GC16767@T430.redhat.com> References: <1393074022-32388-1-git-send-email-pl@kamp.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1393074022-32388-1-git-send-email-pl@kamp.de> Subject: Re: [Qemu-devel] [RFC PATCH] block: optimize zero writes with bdrv_write_zeroes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: kwolf@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com On Sat, 02/22 14:00, Peter Lieven wrote: > this patch tries to optimize zero write requests > by automatically using bdrv_write_zeroes if it is > supported by the format. > > i know that there is a lot of potential for discussion, but i would > like to know what the others think. > > this should significantly speed up file system initialization and > should speed zero write test used to test backend storage performance. > > the difference can simply be tested by e.g. > > dd if=/dev/zero of=/dev/vdX bs=1M > > Signed-off-by: Peter Lieven > --- With this patch, is is still possible to actually do zero fill? Prefill is usually writing zeroes too, but according to the semantic, bdrv_write_zeroes may just set L2 entry flag without allocating clusters, which won't satisfy that. Thanks, Fam