Re: [PATCH 2/2] Documentation: hyperv: Improve synic and interrupt handling description

Easwar Hariharan
2024-05-10T17:54:50Z

On 5/7/2024 6:16 AM, mhkelley58@gmail.com wrote:
> From: Michael Kelley <mhklinux@outlook.com>
>
> Current documentation does not describe how Linux handles the synthetic
> interrupt controller (synic) that Hyper-V provides to guest VMs, nor how
> VMBus or timer interrupts are handled. Add text describing the synic and
> reorganize existing text to make this more clear.
>
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> ---
> Documentation/virt/hyperv/clocks.rst | 21 +++++---
> Documentation/virt/hyperv/vmbus.rst | 79 ++++++++++++++++++----------
> 2 files changed, 66 insertions(+), 34 deletions(-)
>
> diff --git a/Documentation/virt/hyperv/clocks.rst b/Documentation/virt/hyperv/clocks.rst
> index a56f4837d443..919bb92d6d9d 100644
> --- a/Documentation/virt/hyperv/clocks.rst
> +++ b/Documentation/virt/hyperv/clocks.rst
> @@ -62,12 +62,21 @@ shared page with scale and offset values into user space. User
> space code performs the same algorithm of reading the TSC and
> applying the scale and offset to get the constant 10 MHz clock.
>
> -Linux clockevents are based on Hyper-V synthetic timer 0. While
> -Hyper-V offers 4 synthetic timers for each CPU, Linux only uses
> -timer 0. Interrupts from stimer0 are recorded on the "HVS" line in
> -/proc/interrupts. Clockevents based on the virtualized PIT and
> -local APIC timer also work, but the Hyper-V synthetic timer is
> -preferred.
> +Linux clockevents are based on Hyper-V synthetic timer 0 (stimer0).
> +While Hyper-V offers 4 synthetic timers for each CPU, Linux only uses
> +timer 0. In older versions of Hyper-V, an interrupt from stimer0
> +results in a VMBus control message that is demultiplexed by
> +vmbus_isr() as described in the VMBus documentation.

Is VMBus documentation here referring to Documentation/virt/hyperv/vmbus.rst?
If so, could you please add internal links with :ref:? See for example in
Documentation/process/1.Intro.rst. If referring to Microsoft documentation, please
provide a permalink. Please do also look for other opportunities to cross-link within
Documentation or to external resources.

Thanks for the improvements!

Easwar