Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756565Ab0GNCjk (ORCPT ); Tue, 13 Jul 2010 22:39:40 -0400 Received: from mail-ww0-f44.google.com ([74.125.82.44]:45001 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756473Ab0GNCji convert rfc822-to-8bit (ORCPT ); Tue, 13 Jul 2010 22:39:38 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=oLql/Ro4s4krZ9GSUIS4P4YmUJRFW+NyLXQSzVbNmeX32A5CH483xaSZPv0Qtsmhrm lSu4nBxORh0xagS1q3wHWNRmmFVu/XBxRpmjEOYGs2QxwEMAw45OUTt/zdVklTTw2qgj XROd/NMulx8NyVN1FPcspQszjhjVG39ulPzYg= MIME-Version: 1.0 In-Reply-To: <4C3BEBC4.6000902@redhat.com> References: <4C3BEBC4.6000902@redhat.com> Date: Wed, 14 Jul 2010 04:39:35 +0200 Message-ID: Subject: Re: BTRFS: Unbelievably slow with kvm/qemu From: Giangiacomo Mariotti To: Avi Kivity Cc: linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1128 Lines: 27 On Tue, Jul 13, 2010 at 6:29 AM, Avi Kivity wrote: > Btrfs is very slow on sync writes: > > 45KB/s, while 4-5MB/s traffic was actually going to the disk.  For every 4KB > that the the application writes, 400KB+ of metadata is written. > > (It's actually worse, since it starts faster than the average and ends up > slower than the average). > > For kvm, you can try cache=writeback or cache=unsafe and get better > performance (though still slower than ext*). > Yeah, well I've already moved the virtual hd file to an ext3 partition, so the problem for me was actually already "solved" before posting the first post. I posted the first message just to report the particularly bad performances of Btrfs for this test-case, so that, if not already known, they could be investigated and hopefully solved. By the way, thanks to everyone who answered! -- Giangiacomo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/