Re: [PATCH v5 16/16] fs/resctrl: Add documentation on kernel_mode with example

[Luck, Tony]

On Wed, Aug 26, 2026 at 02:32:30PM -0500, Babu Moger wrote:

I fake enabled PLZA on my test system, replacing the wrmsrq()
with some console logging. Tried out several of the examples
in the documentation and the ones I tried all worked.

> +c. Narrow the association to CPUs 0-3
> +::
> +
> +  # echo 0-3 > /sys/fs/resctrl/ctrl1/kmode_cpus_list
> +  # cat /sys/fs/resctrl/ctrl1/kmode_cpus
> +  f
> +  # cat /sys/fs/resctrl/ctrl1/kmode_cpus_list
> +  0-3
> +
> +The write reprograms the association:
> +
> +- CPUs added to the mask are enabled.
> +- CPUs removed from the mask are disabled.

More precise to say:

PLZA is enabled on CPUs added to the mask.
PLZA is disabled on CPUs removed from the mask.

Or perhaps
PLZA reverts to "inherit_user" mode on CPUs removed from the mask.

> +- Offline CPUs in the mask are rejected.
> +- An empty mask disables the association on all currently online CPUs, but
> +  later hotplug CPUs are still associated automatically.

Is there a use case for only enabling PLZA on some subset of CPUs?

The special case for:

# echo "" > ctrl1/kmode_cpus

seems particularly strange. It reads to me as:

"I want this PLZA feature enabled, but don't use it on any CPUs".

-Tony