From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yang Zhang <yang.zhang.wz@gmail.com>
Subject: Re: Enable more than 255 VCPU support without irq remapping function
 in the guest
Date: Tue, 3 May 2016 09:34:31 +0800
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To: Nadav Amit <nadav.amit@gmail.com>
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On 2016/4/29 11:01, Nadav Amit wrote:
> Yang Zhang <yang.zhang.wz@gmail.com> wrote:
>
>> On 2016/4/28 23:32, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote:
>>> I think we are talking about extending KVM's IR-less x2APIC, when
>>> standard x2APIC is the future.
>>
>> Yes, Since IR is only useful for the external device, and 255 CPUs i=
s enough to handle the interrupts from external devices. Besides, i thi=
nk virtual VT-d will bring extra performance impaction for devices, so =
if IR-less X2APIC also works well with more than 255 VCPUs, maybe exten=
ding KVM with IR-less x2apic is not a bad idea.
>
> So will you use x2APIC physical mode in this system?

Probably, cluster mode is the better choice.

> Try not to send a multicast IPI to 400 cores in the VM...

Yes, a multicast IPI to so many cores is a disaster in VM, like=20
flush_tlb_others().


--=20
best regards
yang