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

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-09-20 08:58, Abel Gordon wrote:
> 
> 
> GaoYi <gaoyi709@gmail.com> 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.

Jan

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