Re: [Qemu-devel] Will the ELI incorporated in theKVM?

[Gleb Natapov]

On Thu, Sep 20, 2012 at 09:14:31AM +0200, Jan Kiszka wrote:
> On 2012-09-20 08:58, Abel Gordon wrote:
> > 
> > 
> > GaoYi <address@hidden> wrote on 20/09/2012 08:42:51 AM:
> > 
> >>    The CPU isolation in Hitachi patches is just to improve the real
> >> time performance of GUEST. The core of it, direct IRQ delivery, is
> >> very similar to that of ELI.
> >>     For the ELI patches,
> >>     (1) Since EOI part of ELI is already supported by the Intel
> >> Sandy Bridge CPUs and requires modifications on GUEST code, it
> >> should not be included in the KVM. Only the ELI delivery part, which
> >> plays a vital role in performance improvement, should be considered.
> > 
> > Giving to the guest direct access to the EOI MSR (if x2APIC is available)
> > is what we call "ELI completion". Note this mechanism is not so simple,
> > there are some cases (which are not part of the critical path) where ELI
> > must trap
> > EOIs. For the APLOS paper evaluation we didn't have CPUs with x2APIC so we
> > simulated the behavior changing the guest code.
> > In any case, as you can see in the paper, the big part of the improvement
> > comes from "ELI delivery". "ELI completion" improvement will be
> > even smaller with the latest KVM EOI optimizations for the memory based
> > LAPIC.
> > 
> >>     (2) It should be provided in the kvm-kmod or qemu-kvm ( not just
> >> for some linux kernel as Hitachi patches do), to make this part
> >> independent of linux kernel version.
> > 
> > Exactly, ELI only modifies the kvm kernel module and qemu-kvm but we should
> > also modify VFIO for newer kvm versions.
> 
> Again: If you think the feature is non-invasive, send patches against
> the kernel and QEMU.
> 
And explain why it is better than what modern HW provides.

--
                        Gleb.