Re: [PATCH v5.10/v5.15/v6.1] x86/i8253: Disable PIT timer 0 when not in use

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Feb 18, 2025 at 08:35:23PM +0000, Jay Wang wrote:
> commit 70e6b7d9ae3c63df90a7bba7700e8d5c300c3c60 upstream
> 
> Leaving the PIT interrupt running can cause noticeable steal time for
> virtual guests. The VMM generally has a timer which toggles the IRQ input
> to the PIC and I/O APIC, which takes CPU time away from the guest. Even
> on real hardware, running the counter may use power needlessly (albeit
> not much).
> 
> Make sure it's turned off if it isn't going to be used.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: Michael Kelley <mhkelley@outlook.com>
> Link: https://lore.kernel.org/all/20240802135555.564941-1-dwmw2@infradead.org
> Signed-off-by: Jay Wang <wanjay@amazon.com>
> Cc: stable@vger.kernel.org #v5.10/v5.15/v6.1
> ---
>  arch/x86/kernel/i8253.c     | 11 +++++++++--
>  drivers/clocksource/i8253.c | 13 +++++++++----
>  include/linux/i8253.h       |  1 +
>  3 files changed, 19 insertions(+), 6 deletions(-)

Why don't you also want this in 6.6.y?  You can't submit patches for
only older kernels without them also being in newer ones, otherwise you
will get a regression when upgrading.

Please always submit patches for all relevant kernel trees.

thanks,

greg k-h