linux-kernel - Re: [PATCH v11 07/23] x86/resctrl: Introduce the interface to display monitor mode

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Message-ID: <6d215925-ee84-4b39-b002-9e3b66c015b0@intel.com>
Date: Thu, 6 Feb 2025 10:01:48 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<tony.luck@...el.com>, <peternewman@...gle.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
	<akpm@...ux-foundation.org>, <thuth@...hat.com>, <rostedt@...dmis.org>,
	<xiongwei.song@...driver.com>, <pawan.kumar.gupta@...ux.intel.com>,
	<daniel.sneddon@...ux.intel.com>, <jpoimboe@...nel.org>,
	<perry.yuan@....com>, <sandipan.das@....com>, <kai.huang@...el.com>,
	<xiaoyao.li@...el.com>, <seanjc@...gle.com>, <xin3.li@...el.com>,
	<andrew.cooper3@...rix.com>, <ebiggers@...gle.com>,
	<mario.limonciello@....com>, <james.morse@....com>,
	<tan.shaopeng@...itsu.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <maciej.wieczor-retman@...el.com>,
	<eranian@...gle.com>
Subject: Re: [PATCH v11 07/23] x86/resctrl: Introduce the interface to display
 monitor mode

Hi Babu,

On 1/22/25 12:20 PM, Babu Moger wrote:
> Introduce the interface file "mbm_assign_mode" to list monitor modes
> supported.
> 
> The "mbm_cntr_assign" mode provides the option to assign a counter to
> an RMID, event pair and monitor the bandwidth as long as it is assigned.
> 
> On AMD systems "mbm_cntr_assign" is backed by the ABMC (Assignable

""mbm_cntr_assign" is backed" -> ""mbm_cntr_assign" mode is backed"?

> Bandwidth Monitoring Counters) hardware feature and is enabled by default.
> 
> The "default" mode is the existing monitoring 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 mode on the system.
> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> [mbm_cntr_assign]
> default
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---


> ---
>  Documentation/arch/x86/resctrl.rst     | 26 +++++++++++++++++++++
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 31 ++++++++++++++++++++++++++
>  2 files changed, 57 insertions(+)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index fb90f08e564e..b5defc5bce0e 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -257,6 +257,32 @@ 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":
> +	Reports the list of monitoring modes supported. The enclosed brackets
> +	indicate which mode is enabled.
> +	::
> +
> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> +	  [mbm_cntr_assign]
> +	  default
> +
> +	"mbm_cntr_assign":
> +
> +	In mbm_cntr_assign, monitoring event can only accumulate data while

"In mbm_cntr_assign, monitoring event" -> "In mbm_cntr_assign mode, a monitoring event"?

> +	it is backed by a hardware counter. The user-space is able to specify
> +	which of the events in CTRL_MON or MON groups should have a counter
> +	assigned using the "mbm_assign_control" file. The number of counters
> +	available is described in the "num_mbm_cntrs" file. Changing the mode
> +	may cause all counters on a 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 mbm_cntr_assign mode if supported, because reading
> +	"mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if

Reinette