From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: IO on guest is 20 times slower than host Date: Thu, 26 Mar 2009 12:16:19 +0200 Message-ID: <49CB55F3.5030208@redhat.com> References: <49CA5825.7030201@redhat.com> <4AC00930-1EBB-4704-94CF-29478D07F03A@yoderhome.com> <49CA5D53.1080401@redhat.com> <49CA61E2.3050400@redhat.com> <49CA6FFC.2030807@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Kurt Yoder Return-path: Received: from mx2.redhat.com ([66.187.237.31]:44599 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751041AbZCZKQW (ORCPT ); Thu, 26 Mar 2009 06:16:22 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: Kurt Yoder wrote: > > I see. I looked up another test: using hdparm -t. It doesn't show the > situation as quite so bad, but the guest is still a little over half > the speed of the host: > > me@host:~$ sudo hdparm -t /dev/mapper/HW_RAID-ROOT > > /dev/mapper/HW_RAID-ROOT: > Timing buffered disk reads: 282 MB in 3.00 seconds = 93.92 MB/sec > > me@guest:~# hdparm -t /dev/vda > > /dev/vda: > Timing buffered disk reads: 156 MB in 3.03 seconds = 51.56 MB/sec This is reasonable. IDE emulation is not expected to be as fast as the host. >> Something weird is happening with your system. If you extend the >> test, what does 'top' show? On both guest and host. > > If I extend the test thusly on the guest: > > dd if=/dev/zero of=/bigfile count=10000000 > > I see 100% CPU utilization on the guest, and 100% CPU utilization on > one of the host cores. Can you post 'vmstat 1' snippets on both guest and host while this is running? Oh, and try switching to the deadline I/O scheduler on the host instead of the default cfq. -- error compiling committee.c: too many arguments to function