From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:49082) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rtype-00014B-R1 for qemu-devel@nongnu.org; Sun, 05 Feb 2012 04:56:27 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Rtypd-0006oP-6P for qemu-devel@nongnu.org; Sun, 05 Feb 2012 04:56:26 -0500 Received: from mx1.redhat.com ([209.132.183.28]:16567) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rtypc-0006oG-Vz for qemu-devel@nongnu.org; Sun, 05 Feb 2012 04:56:25 -0500 Message-ID: <4F2E5245.3070400@redhat.com> Date: Sun, 05 Feb 2012 11:56:21 +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> In-Reply-To: <20120205095153.GA29265@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 11:51 AM, Gleb Natapov wrote: > On Sun, Feb 05, 2012 at 11:44:43AM +0200, Avi Kivity wrote: > > On 02/05/2012 11:37 AM, Gleb Natapov wrote: > > > On Thu, Feb 02, 2012 at 06:09:54PM +0200, Avi Kivity wrote: > > > > Device model > > > > ------------ > > > > Currently kvm virtualizes or emulates a set of x86 cores, with or > > > > without local APICs, a 24-input IOAPIC, a PIC, a PIT, and a number of > > > > PCI devices assigned from the host. The API allows emulating the local > > > > APICs in userspace. > > > > > > > > The new API will do away with the IOAPIC/PIC/PIT emulation and defer > > > > them to userspace. Note: this may cause a regression for older guests > > > > that don't support MSI or kvmclock. Device assignment will be done > > > > using VFIO, that is, without direct kvm involvement. > > > > > > > So are we officially saying that KVM is only for modern guest > > > virtualization? > > > > No, but older guests may have reduced performance in some workloads > > (e.g. RHEL4 gettimeofday() intensive workloads). > > > Reduced performance is what I mean. Obviously old guests will continue working. I'm not happy about it either. > > > Also my not so old host kernel uses MSI only for NIC. > > > SATA and USB are using IOAPIC (though this is probably more HW related > > > than kernel version related). > > > > For devices emulated in userspace, it doesn't matter where the IOAPIC > > is. It only matters for kernel provided devices (PIT, assigned devices, > > vhost-net). > > > What about EOI that will have to do additional exit to userspace for each > interrupt delivered? I think the ioapic EOI is asynchronous wrt the core, yes? So the vcpu can just post the EOI broadcast on the apic-bus socketpair, waking up the thread handling the ioapic, and continue running. This trades off vcpu latency for using more host resources. -- error compiling committee.c: too many arguments to function