From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Mueller Subject: Re: Shouldn't cache=none be the default for drives? Date: Thu, 8 Apr 2010 05:07:02 +0000 (UTC) Message-ID: References: <4BBC992D.3050905@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit To: kvm@vger.kernel.org Return-path: Received: from lo.gmane.org ([80.91.229.12]:46802 "EHLO lo.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454Ab0DHFHQ (ORCPT ); Thu, 8 Apr 2010 01:07:16 -0400 Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1NzjxQ-00054I-0T for kvm@vger.kernel.org; Thu, 08 Apr 2010 07:07:12 +0200 Received: from 80-219-107-248.dclient.hispeed.ch ([80.219.107.248]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 08 Apr 2010 07:07:12 +0200 Received: from thomas by 80-219-107-248.dclient.hispeed.ch with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 08 Apr 2010 07:07:12 +0200 Sender: kvm-owner@vger.kernel.org List-ID: Am Wed, 07 Apr 2010 16:39:41 +0200 schrieb Troels Arvin: > Hello, > > I'm conducting some performancetests with KVM-virtualized CentOSes. One > thing I noticed is that guest I/O performance seems to be significantly > better for virtio-based block devices ("drive"s) if the cache=none > argument is used. (This was with a rather powerful storage system > backend which is hard to saturate.) > > So: Why isn't cache=none be the default for drives? while ago i suffered poor performance of virtio and win2008. This helped alot: I enabled "deadline" block scheduler instead of the default "cfq" on the host system. tested with: Host Debian with scheduler deadline, Guest Win2008 with Virtio and cache=none. (26MB/s to 50MB/s boost measured) Maybe this is also true for Linux/Linux. I expect that scheduler "noop" for linux guests would be good. - Thomas