Udo Steinberg <udo@...121...> wrote:
On Fri, 20 Jul 2012 12:22:37 -0700 Julian Stecklina (JS) wrote: JS> Udo, is there an easy way to figure out, if a system supports Interrupt JS> Remapping short of looking into ACPI tables?
You could infer that from looking at the MSI data provided by the hypervisor. Or the hypervisor could announce it in the HIP. But like I said, userland doesn't really need to know.
I meant it more in the way of figuring out which test box to use. :-) ark.intel.com doesn't list this unfortunately.
And yes, correct userland code should be completely oblivious to whether IRQ remapping is used.
JS> > (I'm thinking about adding some code to the hypervisor, causing sem_down to JS> > fail on an interrupt semaphore unless the interrupt has been configured JS> > using assign_gsi.) JS> JS> +1 from me. That would cause broken code to fail early.
The reason I haven't done it yet, is, that it adds a branch to every sem_down on an interrupt semaphore, which is overhead you pay every time, just to get some additional checking at initialization time.
You could enable it only for debug builds, but I don't think it makes any noticeable difference either way.
Julian