Hi Boqun Feng,

On 24/01/2020 06:32, Boqun Feng wrote:

Hi Vincenzo,

[...]

quoted

I had a look to your patches and overall, I could not understand why we can't
use the arch_timer to do the same things you are doing with the one you
introduced in this series. What confuses me is that KVM works just fine with the
arch_timer which was designed with virtualization in mind. Why do we need
another one? Could you please explain?

Please note that the guest VM on Hyper-V for ARM64 doesn't use
arch_timer as the clocksource. See:

	https://lore.kernel.org/linux-arm-kernel/1570129355-16005-7-git-send-email-mikelley@microsoft.com/ (local)

,  ACPI_SIG_GTDT is used for setting up Hyper-V synthetic clocksource
and other initialization work.

I had a look a look at it and my question stands, why do we need another timer
on arm64?

So just to be clear, your suggestion is

1) Hyper-V guest on ARM64 should use arch_timer as clocksource and vDSO
will just work.

or

2) Even though arch_timer is not used as the clocksource, we can still
use it for vDSO.

?

Option #1 would be the preferred solution, unless there is a good reason against.

Regards,
Boqun

-- 
Regards,
Vincenzo