PCIe passthrough really that expensive?

[Harry Schmalzbauer]

 Bezüglich Harry Schmalzbauer's Nachricht vom 09.06.2017 10:22 (localtime):
> Bezüglich Anish's Nachricht vom 08.06.2017 14:35 (localtime):
>> Hi Harry,
>>> I thought I'd save these expensive VM_Exits by using the passthru path.
>> Completely wrong, is it?
>>
>> It depends on which processor you are using. For example APICv was
>> introduced in IvyBridge which enabled h/w assisted localAPIC rather than
>> using s/w emulated, bhyve supports it on Intel processors. 
…
> I'm still usign IvyBridge (E3v2) with this "new" machine, but haven't
> ever heard/thought about APCIv!

It seems APICv is available on IvyBridge-EP (Xeon E5/E7v2) only, not for
E3v2 :-(
Furthermore, if I didn't miss anything in the datasheets, no currently
available E3 Xeon offers local APIC virtualization. Can somebody of the
xperts confirm that?


…
>> Can you run a simple experiment, assign pptdev interrupts to core that's
>> not running guest/vcpu? This will reduce #VMEXIT on vcpu which we know
>> is expensive.
> Interesting approach.  But I have no idea how I should assign a PCIe
> specific core to a PCIe dev.  Is it pptdev specific? The tunables in
> device.hints(5) can't be used for that, can they?

I wasn't able to find out how to do that.
Any hints highly appreciated!

-harry