From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir Bashkirtsev Subject: Poor read performance in KVM Date: Sun, 15 Jul 2012 22:43:57 +0930 Message-ID: <5002C215.108@bashkirtsev.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail.logics.net.au ([150.101.56.178]:59099 "EHLO mail.logics.net.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751624Ab2GONOX (ORCPT ); Sun, 15 Jul 2012 09:14:23 -0400 Received: from x.logics.net.au (gw.logics.net.au [150.101.235.251] (may be forged)) (authenticated bits=0) by mail.logics.net.au (8.14.5/8.14.1) with ESMTP id q6FDDvKo003609 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO) for ; Sun, 15 Jul 2012 22:43:58 +0930 Sender: ceph-devel-owner@vger.kernel.org List-ID: To: ceph-devel@vger.kernel.org Hello, Lately I was trying to get KVM to perform well on RBD. But it still appears elusive. [root@alpha etc]# rados -p rbd bench 120 seq -t 8 Total time run: 16.873277 Total reads made: 302 Read size: 4194304 Bandwidth (MB/sec): 71.592 Average Latency: 0.437984 Max latency: 3.26817 Min latency: 0.015786 Fairly good performance. But when I run in KVM: [root@mail ~]# hdparm -tT /dev/vda /dev/vda: Timing cached reads: 8808 MB in 2.00 seconds = 4411.49 MB/sec Timing buffered disk reads: 10 MB in 6.21 seconds = 1.61 MB/sec Not even close to what rados bench show! I even seen 900KB/sec performance. Such slow read performance of course affecting guests. Any ideas where to start to look for performance boost? Regards, Vladimir