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

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Message-ID: <807443f4-2442-4925-becc-6eb20887acf6@linux.microsoft.com>
Date: Fri, 10 May 2024 10:54:49 -0700
From: Easwar Hariharan <eahariha@...ux.microsoft.com>
To: mhklinux@...look.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, kys@...rosoft.com, corbet@....net,
 linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2] Documentation: hyperv: Improve synic and interrupt
 handling description

On 5/7/2024 6:16 AM, mhkelley58@...il.com wrote:
> From: Michael Kelley <mhklinux@...look.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@...look.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