linux-kernel - Re: [RFC] Next gen kvm api

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Date:	Sun, 05 Feb 2012 11:44:43 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	KVM list <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [RFC] Next gen kvm api

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).

> 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).

-- 
error compiling committee.c: too many arguments to function

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