On 8/27/2013 1:41 AM, Jan Beulich wrote:

On 27.08.13 at 03:21, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> wrote:

I have been trying to test out this patch.  Somehow, I could not get Xen 
boot option to exercise the code path.  What boot configuration are you 
using to test this?

I don't have a system suitable for testing this; Sander did. The main
requirement apart from having an IOMMU is to also have a HPET
with at least on MSI-capable channel. Otherwise code won't get
here. The normal flow is 

hpet_broadcast_init() -> hpet_fsb_cap_lookup() -> hpet_assign_irq()
-> hpet_setup_msi_irq() -> iommu_setup_hpet_msi()

Jan

Ah, ok.. I found out that this only applies on the family10h system with IOMMU due to the check in arch/x86/time.c:_disable_pit_irq "if (!boot_cpu_has(X86_FEATURE_ARAT))" and the condition in arch/x86/cpu/amd.c:_init_amd() /* * Family 0x12 and above processors have APIC timer * running in deep C states. */ if (c->x86 > 0x11) set_bit(X86_FEATURE_ARAT, c->x86_capability); Jan, do you think you could also add the comment that this only applicable on family10h? Acked-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Thank you, Suravee.