linux-kernel - Re: [PATCH v15 24/34] fs/resctrl: Report 'Unassigned' for MBM events in mbm

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Message-ID: <4b5eef45-9110-47f7-8e1b-a59028d66c52@intel.com>
Date: Thu, 17 Jul 2025 20:53:49 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<james.morse@....com>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <x86@...nel.org>, <hpa@...or.com>,
	<akpm@...ux-foundation.org>, <paulmck@...nel.org>, <rostedt@...dmis.org>,
	<Neeraj.Upadhyay@....com>, <david@...hat.com>, <arnd@...db.de>,
	<fvdl@...gle.com>, <seanjc@...gle.com>, <jpoimboe@...nel.org>,
	<pawan.kumar.gupta@...ux.intel.com>, <xin@...or.com>,
	<manali.shukla@....com>, <tao1.su@...ux.intel.com>, <sohil.mehta@...el.com>,
	<kai.huang@...el.com>, <xiaoyao.li@...el.com>, <peterz@...radead.org>,
	<xin3.li@...el.com>, <kan.liang@...ux.intel.com>,
	<mario.limonciello@....com>, <thomas.lendacky@....com>, <perry.yuan@....com>,
	<gautham.shenoy@....com>, <chang.seok.bae@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>, <eranian@...gle.com>
Subject: Re: [PATCH v15 24/34] fs/resctrl: Report 'Unassigned' for MBM events
 in mbm_event mode

Hi Babu,

On 7/8/25 3:17 PM, Babu Moger wrote:
> When the "mbm_event" counter assignment mode is enabled, a hardware counter
> must be assigned to read the event.
> 
> Report 'Unassigned' in case the user attempts to read the event without
> assigning a hardware counter.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---



> ---
>  Documentation/filesystems/resctrl.rst | 8 ++++++++
>  fs/resctrl/ctrlmondata.c              | 6 ++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 446736dbd97f..4f5eb5bbd4b5 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -434,6 +434,14 @@ When monitoring is enabled all MON groups will also contain:
>  	for the L3 cache they occupy). These are named "mon_sub_L3_YY"
>  	where "YY" is the node number.
>  
> +	The "mbm_event" counter assignment mode offers "num_mbm_cntrs" number of
> +	counters and allows users to assign counters to mon_hw_id, event pairs
> +	enabling bandwidth monitoring for as long as the counter remains assigned.
> +	The hardware will continue tracking the assigned counter until the user
> +	manually unassigns it, ensuring that event data is not reset during this
> +	period. An MBM event returns 'Unassigned' when the event does not have
> +	a hardware counter assigned.

Most of this duplicates the "mbm_event" description added in patch #10. It should just
be sufficient to mention that this applies to "mbm_event" counter assignment mode
and then user can look up the main description in the doc.

The last sentence is related to this section and need an update to reflect behavior
when a CTRL_MON event is read and it or some of the MON groups do not have
counters assigned. The paragraph that precedes this does describe how the sum
works so this can tie into that.


> +
>  "mon_hw_id":
>  	Available only with debug option. The identifier used by hardware
>  	for the monitor group. On x86 this is the RMID.
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index ce766b2cdfc1..45351673e4ee 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -661,10 +661,16 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>  
>  checkresult:
>  
> +	/*
> +	 * -ENOENT is a special case, set only when "mbm_event" counter assignment
> +	 * mode is enabled and no counter has been assigned.
> +	 */
>  	if (rr.err == -EIO)
>  		seq_puts(m, "Error\n");
>  	else if (rr.err == -EINVAL)
>  		seq_puts(m, "Unavailable\n");
> +	else if (rr.err == -ENOENT)
> +		seq_puts(m, "Unassigned\n");
>  	else
>  		seq_printf(m, "%llu\n", rr.val);
>  

As mentioned in previous patch, please squash with previous patch.

Reinette