Re: [patch 26/26] x64, x2apic/intr-remap: introduce CONFIG_INTR_REMAP

[Suresh Siddha]

On Thu, Jul 10, 2008 at 04:37:33PM -0700, Yong Wang wrote:
> > Is it possible to run in x2apic mode without running in interrupt remapping mode?
> > Just send the irqs directly to the cpu?  It feels like it should be if an iommu
> > doesn't get in the way.
> >
> 
> Yes, it is possible to run in x2apic mode without intr-remap. However, the extended
> cpu addressability will not be fully utilized that way.

No. CPU can't be in x2apic mode with out enabling interrupt-remapping.
Interrupts may not work (even when we have few cpu's). For example, in logical
cluster mode, logical x2apic id (initialized by HW) will be > 16 bit,
in a smaller DP configuration.

In general, enabling x2apic with out enabling interrupt-remapping is not
recommended, as the platform will be using legacy interrupt format and the
CPU will be using extended ID mode.

thanks,
suresh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/