From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] Ideas wiki for GSoC 2010 Date: Mon, 15 Mar 2010 17:06:57 +0200 Message-ID: <4B9E4D11.70402@redhat.com> References: <20100310183023.6632aece@redhat.com> <4B9E2745.7060903@redhat.com> <20100315125313.GK9457@il.ibm.com> <20100315130310.GE13108@8bytes.org> <4B9E320E.7040605@redhat.com> <4B9E34E1.3090709@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Joerg Roedel , Muli Ben-Yehuda , Luiz Capitulino , qemu-devel@nongnu.org, aliguori@us.ibm.com, kvm@vger.kernel.org, jan.kiszka@siemens.com, agraf@suse.de, agl@us.ibm.com, Nadav Amit , Ben-Ami Yassour1 To: Anthony Liguori Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36077 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964955Ab0COPHR (ORCPT ); Mon, 15 Mar 2010 11:07:17 -0400 In-Reply-To: <4B9E34E1.3090709@codemonkey.ws> Sender: kvm-owner@vger.kernel.org List-ID: On 03/15/2010 03:23 PM, Anthony Liguori wrote: > On 03/15/2010 08:11 AM, Avi Kivity wrote: >> On 03/15/2010 03:03 PM, Joerg Roedel wrote: >>> >>>>> I will add another project - iommu emulation. Could be very useful >>>>> for doing device assignment to nested guests, which could make >>>>> testing a lot easier. >>>> Our experiments show that nested device assignment is pretty much >>>> required for I/O performance in nested scenarios. >>> Really? I did a small test with virtio-blk in a nested guest (disk read >>> with dd, so not a real benchmark) and got a reasonable read-performance >>> of around 25MB/s from the disk in the l2-guest. >>> >> >> Your guest wasn't doing a zillion VMREADs and VMWRITEs every exit. >> >> I plan to reduce VMREAD/VMWRITE overhead for kvm, but not much we can >> do for other guests. > > VMREAD/VMWRITEs are generally optimized by hypervisors as they tend to > be costly. KVM is a bit unusual in terms of how many times the > instructions are executed per exit. Do you know offhand of any unnecessary read/writes? There's update_cr8_intercept(), but on normal exits, I don't see what else we can remove. -- error compiling committee.c: too many arguments to function