From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: KVM performance vs. Xen Date: Thu, 30 Apr 2009 10:11:26 -0500 Message-ID: <49F9BF9E.50006@codemonkey.ws> References: <49F8672E.5080507@linux.vnet.ibm.com> <49F967AE.4040905@redhat.com> <49F9AB64.20506@codemonkey.ws> <49F9AEC0.2060909@redhat.com> <49F9AFE6.8010704@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Avi Kivity , kvm-devel To: Andrew Theurer Return-path: Received: from mail-qy0-f196.google.com ([209.85.221.196]:45480 "EHLO mail-qy0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756355AbZD3PL3 (ORCPT ); Thu, 30 Apr 2009 11:11:29 -0400 Received: by qyk34 with SMTP id 34so2419868qyk.33 for ; Thu, 30 Apr 2009 08:11:29 -0700 (PDT) In-Reply-To: <49F9AFE6.8010704@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Andrew Theurer wrote: > Avi Kivity wrote: >> Anthony Liguori wrote: >>> Avi Kivity wrote: >>>>> >>>>> 1) I'm seeing about 2.3% in scheduler functions [that I recognize]. >>>>> Does that seems a bit excessive? >>>> >>>> Yes, it is. If there is a lot of I/O, this might be due to the >>>> thread pool used for I/O. >>> >>> This is why I wrote the linux-aio patch. It only reduced CPU >>> consumption by about 2% although I'm not sure if that's absolute or >>> relative. Andrew? > If I recall correctly, it was 2.4% and relative. But with 2.3% in > scheduler functions, that's what I expected. >> >> Was that before or after the entire path was made copyless? > If this is referring to the preadv/writev support, no, I have not > tested with that. Previously, the block API only exposed non-vector interfaces and bounced vectored operations to a linear buffer. That's been eliminated now though so we need to update the linux-aio patch to implement a vectored backend interface. However, it is an apples to apples comparison in terms of copying since the same is true with the thread pool. My take away was that the thread pool overhead isn't the major source of issues. Regards, Anthony Liguori