From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM performance vs. Xen Date: Thu, 30 Apr 2009 16:52:02 +0300 Message-ID: <49F9AD02.8070902@redhat.com> References: <49F8672E.5080507@linux.vnet.ibm.com> <49F967AE.4040905@redhat.com> <49F99E6A.3060404@linux.vnet.ibm.com> <49F9A160.3030609@redhat.com> <49F9AB2F.4020505@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm-devel To: Andrew Theurer Return-path: Received: from mx2.redhat.com ([66.187.237.31]:45503 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763735AbZD3NwG (ORCPT ); Thu, 30 Apr 2009 09:52:06 -0400 In-Reply-To: <49F9AB2F.4020505@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Andrew Theurer wrote: > >> >>> disk: read: 17 MB/sec write: 40 MB/sec >> >> This could definitely cause the extra load, especially if it's many >> small requests (compared to a few large ones). > I don't have the request sizes at my fingertips, but we have to use a > lot of disks to support this I/O, so I think it's safe to assume there > are a lot more requests than a simple large sequential read/write. Yes. Well the high context switch rate is the scheduler's way of telling us to use linux-aio. If "lot's of disks" == 100, with a 3ms seek time, that's already 60,000 cs/sec. >> Really, I think linux-aio support can help here. > Yes, I think that would work for real block devices, but would that > help for files? I am using real block devices right now, but it would > be nice to also see a benefit for files in a file-system. Or maybe I > am mis-understanding this, and linux-aio can be used on files? It could work with files with cache=none (though not qcow2 as now written). -- error compiling committee.c: too many arguments to function