From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: windows PIO question Date: Sun, 05 Feb 2012 17:10:55 +0200 Message-ID: <4F2E9BFF.1050700@redhat.com> References: <20120202211630.GA4719@nik-comp.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm To: Nikola Ciprich Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6514 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754182Ab2BEPLW (ORCPT ); Sun, 5 Feb 2012 10:11:22 -0500 In-Reply-To: <20120202211630.GA4719@nik-comp.lan> Sender: kvm-owner@vger.kernel.org List-ID: On 02/02/2012 11:16 PM, Nikola Ciprich wrote: > Hello everybody, > > I'm a bit confused regarding windows guests and PIO.. some time ago, I was trying > to find out, why one of my windows guests was running terribly slow. > After checking the trace-cmd output, Avi stated that windows were using PIO instead > of DMA, after changing that, windows indeed got a lot faster. I didn't check traces > after that, but I'm now testing host with two windows 2003 guests, and checking the > trac-cmd output, I see a lot of kvm_pio calls. > While windows don't seem to be running particularly slow, they're not especially > fast either, and I'm wandering whether this could be related. But checking IDE > bus in guests, they seem to be using DMA which confuses me... > so my questions is, what are the kvm_pio operations I see in traces, and how can > I tell what is OK and what is wrong, regarding disks DMA/PIO? > If somebody could shed some light on this for me, I'd be very grateful... Not all PIO operations are DMA. Provide a trace and we can look. -- error compiling committee.c: too many arguments to function