Problem? intel_iommu=off; perf top shows acpi_os_read_port asextremely busy

[Michael Breuer]

Having given up for now on VT-D, I rebooted 2.6.38 rc8 with 
intel_iommu=off. Whilst my myriad of broken bios issues cleared, I now 
see in perf top acpi_os_read_port as continually the busiest function. 
With intel_iommu enabled, _spin_lock was always on top, and nothing else 
was notable.

This seems odd to me, perhaps this will make sense to someone else.

FWIW, I'm running on an Asus p6t deluxe v2; ht enabled; no errors or 
oddities in dmesg or /var/log/messages.
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