> But doesn't the interrupt code have to check all interrupt sources on a 
> shared line? 

well technically the kernel just calls all handers.

>  That means checking the non-PV interrupt as well, which 
> involves a vmexit (for mmio read).

ok I see what you mean. Yes agreed we should avoid sharing with one of
those animals ;)
(Shouldn't be hard since we control the bios, and it's always fake
hardware anyway)


> It is possible (Xen does it) to batch interrupt delivery so that 
> multiple interrupts can be delivered with one vmentry.  So you get the 
> best of both worlds: one check for interrupt source, and one vmentry if 
> multiple interrupts have fired.

check for interrupt source is really cheap. I bet it's cheaper than the
hacks xen does. (xen does many things that in academic 1970's
hypervisors were a win but aren't on modern hardware..)

Don't get me wrong, batching is probably a win, just it shouldn't be too
expensive in terms of overhead or you'll loose anyway over time.


> 

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via 
http://www.linuxfirmwarekit.org


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