From: "Luck, Tony" <tony.luck@intel.com>
To: Babu Moger <babu.moger@amd.com>
Cc: <reinette.chatre@intel.com>, <Dave.Martin@arm.com>,
<james.morse@arm.com>, <bp@alien8.de>, <ben.horgan@arm.com>,
<corbet@lwn.net>, <skhan@linuxfoundation.org>,
<rdunlap@infradead.org>, <tglx@kernel.org>, <mingo@redhat.com>,
<dave.hansen@linux.intel.com>, <hpa@zytor.com>,
<fenghuay@nvidia.com>, <akpm@linux-foundation.org>,
<rppt@kernel.org>, <dapeng1.mi@linux.intel.com>,
<elver@google.com>, <jlayton@kernel.org>,
<enelsonmoore@gmail.com>, <kuba@kernel.org>,
<ebiggers@kernel.org>, <seanjc@google.com>,
<peterz@infradead.org>, <chao.gao@intel.com>,
<jmattson@google.com>, <naveen@kernel.org>,
<ricardo.neri-calderon@linux.intel.com>, <tiala@microsoft.com>,
<chang.seok.bae@intel.com>, <prathyushi.nangia@amd.com>,
<kim.phillips@amd.com>, <elena.reshetova@intel.com>,
<darwi@linutronix.de>, <linux-doc@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <x86@kernel.org>
Subject: Re: [PATCH v5 16/16] fs/resctrl: Add documentation on kernel_mode with example
Date: Tue, 1 Sep 2026 14:14:02 -0700 [thread overview]
Message-ID: <apdAGiN6zvIDU1kD@agluck-desk3> (raw)
In-Reply-To: <c04c7a9e2e47d472c6cf4b184ef9c3be5ef6b4c8.1787772750.git.babu.moger@amd.com>
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
next prev parent reply other threads:[~2026-09-01 21:14 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-26 19:32 [PATCH v5 00/16] x86/resctrl: Add kernel-mode (e.g., PLZA) support to the resctrl subsystem Babu Moger
2026-08-26 19:32 ` [PATCH v5 01/16] x86/cpufeatures: Support Privilege Level Zero Association (PLZA) Babu Moger
2026-08-26 19:32 ` [PATCH v5 02/16] x86/resctrl: Add PLZA support to command-line options Babu Moger
2026-08-26 19:32 ` [PATCH v5 03/16] x86/resctrl: Add PLZA configuration definitions and data structures Babu Moger
2026-08-26 19:32 ` [PATCH v5 04/16] fs/resctrl: Introduce kernel mode policy enum Babu Moger
2026-08-26 19:32 ` [PATCH v5 05/16] x86,fs/resctrl: Introduce architecture hooks to program kernel mode Babu Moger
2026-08-26 19:32 ` [PATCH v5 06/16] fs/resctrl: Introduce kernel mode states for resctrl Babu Moger
2026-08-26 19:32 ` [PATCH v5 07/16] fs/resctrl: Introduce resctrl_set_kmode_support() to register supported modes Babu Moger
2026-08-26 19:32 ` [PATCH v5 08/16] x86/resctrl: Expose assign_global_enable_per_cpu when PLZA is available Babu Moger
2026-08-26 19:32 ` [PATCH v5 09/16] fs/resctrl: Add interface to display supported and active kernel modes Babu Moger
2026-08-26 19:32 ` [PATCH v5 10/16] fs/resctrl: Add support for hidden resource group files Babu Moger
2026-08-26 19:32 ` [PATCH v5 11/16] fs/resctrl: Introduce kmode_cpus/kmode_cpus_list per rdtgroup Babu Moger
2026-08-26 19:32 ` [PATCH v5 12/16] fs/resctrl: Program kernel mode assignments on CPU hotplug Babu Moger
2026-08-26 19:32 ` [PATCH v5 13/16] fs/resctrl: Deactivate the kernel mode association when a group is removed Babu Moger
2026-08-26 19:32 ` [PATCH v5 14/16] fs/resctrl: Add interface to modify kernel mode via info/kernel_mode Babu Moger
2026-08-26 19:32 ` [PATCH v5 15/16] fs/resctrl: Allow user space to write kmode_cpus/kmode_cpus_list Babu Moger
2026-08-26 19:32 ` [PATCH v5 16/16] fs/resctrl: Add documentation on kernel_mode with example Babu Moger
2026-09-01 21:14 ` Luck, Tony [this message]
2026-09-01 23:28 ` Moger, Babu
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