From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: *terrible* speed of savevm/loadvm/delvm Date: Sun, 23 Nov 2008 15:51:41 +0200 Message-ID: <49295FED.9020602@redhat.com> References: <491B0F4B.9060502@msgid.tls.msk.ru> <491C1E8C.3070701@redhat.com> <4925B5C4.1030008@msgid.tls.msk.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: KVM list To: Michael Tokarev Return-path: Received: from mx2.redhat.com ([66.187.237.31]:43979 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758059AbYKWNvx (ORCPT ); Sun, 23 Nov 2008 08:51:53 -0500 In-Reply-To: <4925B5C4.1030008@msgid.tls.msk.ru> Sender: kvm-owner@vger.kernel.org List-ID: Michael Tokarev wrote: >>> As you see, it writes 2 bytes, llseeks to THE SAME >>> position, writes next 2 bytes and so on. This takes >>> HUGE amount of time, and can be done, in most cases, >>> in a single write without any seeks. >>> >>> Is it just me or are savevm/loadvm/delvm really THAT >>> broken? >>> >> It's qcow2 that is broken, with the new default cache=writethrough. >> Does cache=writeback speed things up? >> > > Please excuse me for this long delay replying... > I tried other solutions meanwhile (migrate to exec:), but did not > succeed there either. > > Well. While with writeback mode, the speed is definitely > better. But it is still very very slow - not THAT terrible, > but it still takes several mins to complete a 512MB VM with > a single 4Gb qcow2 file. > Any idea what is happening? Is it disk bound, or cpu bound? It shouldn't be that slow with writeback. -- error compiling committee.c: too many arguments to function