linux-kernel - Re: [PATCH v14 11/32] fs/resctrl: Introduce the interface to display monitoring modes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <94825e50-1f8d-4612-bdab-33db756a19a8@intel.com>
Date: Tue, 24 Jun 2025 15:47:09 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <akpm@...ux-foundation.org>,
	<rostedt@...dmis.org>, <paulmck@...nel.org>, <thuth@...hat.com>,
	<ardb@...nel.org>, <gregkh@...uxfoundation.org>, <seanjc@...gle.com>,
	<thomas.lendacky@....com>, <pawan.kumar.gupta@...ux.intel.com>,
	<manali.shukla@....com>, <perry.yuan@....com>, <kai.huang@...el.com>,
	<peterz@...radead.org>, <xiaoyao.li@...el.com>, <kan.liang@...ux.intel.com>,
	<mario.limonciello@....com>, <xin3.li@...el.com>, <gautham.shenoy@....com>,
	<xin@...or.com>, <chang.seok.bae@...el.com>, <fenghuay@...dia.com>,
	<peternewman@...gle.com>, <maciej.wieczor-retman@...el.com>,
	<eranian@...gle.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 11/32] fs/resctrl: Introduce the interface to display
 monitoring modes

Hi Babu,

On 6/13/25 2:04 PM, Babu Moger wrote:
> Introduce the resctrl file "mbm_assign_mode" to list the supported
> monitoring modes.

"the supported monitoring modes" -> "the supported counter assignment modes"?

> 
> The "mbm_event" mode allows users to assign a hardware counter ID to an

nit: users do not assign/pick the ID, this is done by resctrl. So perhaps
just "users to assign a hardware counter to ..."

> RMID, event pair and monitor bandwidth usage as long as it is assigned.
> The hardware continues to track the assigned counter until it is
> explicitly unassigned by the user. Each event within a resctrl group
> can be assigned independently in this mode.
> 
> On AMD systems "mbm_event" mode is backed by the ABMC (Assignable
> Bandwidth Monitoring Counters) hardware feature and is enabled by default.
> 
> The "default" mode is the existing mode that works without the explicit
> counter assignment, instead relying on dynamic counter assignment by
> hardware that may result in hardware not dedicating a counter resulting
> in monitoring data reads returning "Unavailable".
> 
> Provide an interface to display the monitor modes on the system.
> 
> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> [mbm_event]
> default
> 
> Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check to support Arm64.
> 
> On x86, CONFIG_RESCTRL_ASSIGN_FIXED is not defined. On Arm64, it will be
> defined when the "mbm_event" mode is supported.
> 
> Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check early to ensure the user
> interface remains compatible with upcoming Arm64 support. IS_ENABLED()
> safely evaluates to 0 when the configuration is not defined.
> 
> As a result, for MPAM, the display would be either:
> [default]
> or
> [mbm_event]
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---

...

> ---
>  Documentation/filesystems/resctrl.rst | 31 ++++++++++++++++++++++
>  fs/resctrl/rdtgroup.c                 | 37 +++++++++++++++++++++++++++
>  2 files changed, 68 insertions(+)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index c97fd77a107d..4e76e4ac5d3a 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -257,6 +257,37 @@ with the following files:
>  	    # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
>  	    0=0x30;1=0x30;3=0x15;4=0x15
>  
> +"mbm_assign_mode":
> +	The supported monitoring modes. The enclosed brackets indicate which mode

"The supported monitoring modes." -> "The supported counter assignment modes."?

> +	is enabled.
> +	::
> +
> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +	  [mbm_event]
> +	  default
> +
> +	"mbm_event":
> +
> +	mbm_event mode allows users to assign a hardware counter ID to an RMID, event

"hardware counter ID" -> "hardware counter"

> +	pair and monitor the bandwidth usage as long as it is assigned. The hardware
> +	continues to track the assigned counter until it is explicitly unassigned by
> +	the user. Each event within a resctrl group can be assigned independently.
> +
> +	In this mode, a monitoring event can only accumulate data while it is backed
> +	by a hardware counter. Use "mbm_L3_assignments" found in each CTRL_MON and MON
> +	group to specify which of the events should have a counter assigned. The number
> +	of counters available is described in the "num_mbm_cntrs" file. Changing the
> +	mode may cause all counters on the resource to reset.
> +
> +	"default":
> +
> +	In default mode, resctrl assumes there is a hardware counter for each
> +	event within every CTRL_MON and MON group. On AMD platforms, it is
> +	recommended to use the mbm_event mode, if supported, to prevent reset of MBM
> +	events between reads resulting from hardware re-allocating counters. This can
> +	result in misleading values or display "Unavailable" if no counter is assigned
> +	to the event.
> +
>  "max_threshold_occupancy":
>  		Read/write file provides the largest value (in
>  		bytes) at which a previously used LLC_occupancy

Reinette