From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC] Next gen kvm api Date: Sun, 05 Feb 2012 15:16:38 +0200 Message-ID: <4F2E8136.2060408@redhat.com> References: <4F2AB552.2070909@redhat.com> <20120205093723.GQ23536@redhat.com> <4F2E4F8B.8090504@redhat.com> <20120205095153.GA29265@redhat.com> <4F2E5245.3070400@redhat.com> <20120205105804.GS23536@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-kernel , KVM list , qemu-devel To: Gleb Natapov Return-path: In-Reply-To: <20120205105804.GS23536@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org On 02/05/2012 12:58 PM, Gleb Natapov wrote: > > > > > > > Reduced performance is what I mean. Obviously old guests will continue working. > > > > I'm not happy about it either. > > > It is not only about old guests either. In RHEL we pretend to not > support HPET because when some guests detect it they are accessing > its mmio frequently for certain workloads. For Linux guests we can > avoid that by using kvmclock. For Windows guests I hope we will have > enlightenment timers + RTC, but what about other guests? *BSD? How often > they access HPET when it is available? We will probably have to move > HPET into the kernel if we want to make it usable. If we have to, we'll do it. > So what is the criteria for device to be emulated in userspace vs kernelspace > in new API? Never? What about vhost-net then? Only if a device works in MSI > mode? This may work for HPET case, but looks like artificial limitation > since the problem with HPET is not interrupt latency, but mmio space > access. The criteria is, if it's absolutely necessary. > And BTW, what about enlightenment timers for Windows? Are we going to > implement them in userspace or kernel? The kernel. -- error compiling committee.c: too many arguments to function From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754671Ab2BENQo (ORCPT ); Sun, 5 Feb 2012 08:16:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:13385 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753980Ab2BENQn (ORCPT ); Sun, 5 Feb 2012 08:16:43 -0500 Message-ID: <4F2E8136.2060408@redhat.com> Date: Sun, 05 Feb 2012 15:16:38 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: Gleb Natapov CC: KVM list , linux-kernel , qemu-devel Subject: Re: [RFC] Next gen kvm api References: <4F2AB552.2070909@redhat.com> <20120205093723.GQ23536@redhat.com> <4F2E4F8B.8090504@redhat.com> <20120205095153.GA29265@redhat.com> <4F2E5245.3070400@redhat.com> <20120205105804.GS23536@redhat.com> In-Reply-To: <20120205105804.GS23536@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/05/2012 12:58 PM, Gleb Natapov wrote: > > > > > > > Reduced performance is what I mean. Obviously old guests will continue working. > > > > I'm not happy about it either. > > > It is not only about old guests either. In RHEL we pretend to not > support HPET because when some guests detect it they are accessing > its mmio frequently for certain workloads. For Linux guests we can > avoid that by using kvmclock. For Windows guests I hope we will have > enlightenment timers + RTC, but what about other guests? *BSD? How often > they access HPET when it is available? We will probably have to move > HPET into the kernel if we want to make it usable. If we have to, we'll do it. > So what is the criteria for device to be emulated in userspace vs kernelspace > in new API? Never? What about vhost-net then? Only if a device works in MSI > mode? This may work for HPET case, but looks like artificial limitation > since the problem with HPET is not interrupt latency, but mmio space > access. The criteria is, if it's absolutely necessary. > And BTW, what about enlightenment timers for Windows? Are we going to > implement them in userspace or kernel? The kernel. -- error compiling committee.c: too many arguments to function From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:33887) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ru1xU-0007lN-Tn for qemu-devel@nongnu.org; Sun, 05 Feb 2012 08:16:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ru1xT-0003QI-Mt for qemu-devel@nongnu.org; Sun, 05 Feb 2012 08:16:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35484) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ru1xT-0003QE-Au for qemu-devel@nongnu.org; Sun, 05 Feb 2012 08:16:43 -0500 Message-ID: <4F2E8136.2060408@redhat.com> Date: Sun, 05 Feb 2012 15:16:38 +0200 From: Avi Kivity MIME-Version: 1.0 References: <4F2AB552.2070909@redhat.com> <20120205093723.GQ23536@redhat.com> <4F2E4F8B.8090504@redhat.com> <20120205095153.GA29265@redhat.com> <4F2E5245.3070400@redhat.com> <20120205105804.GS23536@redhat.com> In-Reply-To: <20120205105804.GS23536@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC] Next gen kvm api List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: linux-kernel , KVM list , qemu-devel On 02/05/2012 12:58 PM, Gleb Natapov wrote: > > > > > > > Reduced performance is what I mean. Obviously old guests will continue working. > > > > I'm not happy about it either. > > > It is not only about old guests either. In RHEL we pretend to not > support HPET because when some guests detect it they are accessing > its mmio frequently for certain workloads. For Linux guests we can > avoid that by using kvmclock. For Windows guests I hope we will have > enlightenment timers + RTC, but what about other guests? *BSD? How often > they access HPET when it is available? We will probably have to move > HPET into the kernel if we want to make it usable. If we have to, we'll do it. > So what is the criteria for device to be emulated in userspace vs kernelspace > in new API? Never? What about vhost-net then? Only if a device works in MSI > mode? This may work for HPET case, but looks like artificial limitation > since the problem with HPET is not interrupt latency, but mmio space > access. The criteria is, if it's absolutely necessary. > And BTW, what about enlightenment timers for Windows? Are we going to > implement them in userspace or kernel? The kernel. -- error compiling committee.c: too many arguments to function