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

[Abel Gordon]

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.