linux-kernel - Re: [PATCH v12 09/26] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <c149c6f9-cb72-4737-b4e3-34ee990fdc9f@intel.com>
Date: Fri, 11 Apr 2025 14:01:02 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <tony.luck@...el.com>,
	<peternewman@...gle.com>
CC: <corbet@....net>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
	<hpa@...or.com>, <paulmck@...nel.org>, <akpm@...ux-foundation.org>,
	<thuth@...hat.com>, <rostedt@...dmis.org>, <ardb@...nel.org>,
	<gregkh@...uxfoundation.org>, <daniel.sneddon@...ux.intel.com>,
	<jpoimboe@...nel.org>, <alexandre.chartre@...cle.com>,
	<pawan.kumar.gupta@...ux.intel.com>, <thomas.lendacky@....com>,
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	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<maciej.wieczor-retman@...el.com>, <eranian@...gle.com>
Subject: Re: [PATCH v12 09/26] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Babu,

On 4/3/25 5:18 PM, Babu Moger wrote:
> The mbm_cntr_assign mode provides an option to the user to assign a
> counter to an RMID, event pair and monitor the bandwidth as long as
> the counter is assigned. Number of assignments depend on number of
> monitoring counters available.
> 
> Provide the interface to display the number of monitoring counters

An interface can also be a function. To help make this work obvious
it can be specific:

	Create 'num_mbm_cntrs' resctrl file that displays the number of
	monitoring counters supported in each domain. 'num_mbm_cntrs'
	is only visible to user space when the system supports
	mbm_cntr_assign mode.

> supported in each domain. The resctrl file 'num_mbm_cntrs' is visible
> to user space when the system supports mbm_cntr_assign mode.
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
...

> ---
>  Documentation/arch/x86/resctrl.rst     | 11 ++++++++++
>  arch/x86/kernel/cpu/resctrl/monitor.c  |  3 +++
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 30 ++++++++++++++++++++++++++
>  3 files changed, 44 insertions(+)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index bb96b44019fe..35d908befdfb 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -284,6 +284,17 @@ with the following files:
>  	misleading values or display "Unavailable" if no counter is assigned
>  	to the event.
>  
> +"num_mbm_cntrs":
> +	The maximum number of monitoring counters (total of available and assigned
> +	counters) in each domain when the system supports mbm_cntr_assign mode.
> +
> +	For example, on a system with maximum of 32 memory bandwidth monitoring
> +	counters in each of its L3 domains:
> +	::
> +
> +	  # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
> +	  0=32;1=32
> +
>  "max_threshold_occupancy":
>  		Read/write file provides the largest value (in
>  		bytes) at which a previously used LLC_occupancy
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 6ed7e51d3fdb..028b49878ad0 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1234,6 +1234,9 @@ int __init resctrl_mon_resource_init(void)
>  	else if (resctrl_arch_is_mbm_total_enabled())
>  		mba_mbps_default_event = QOS_L3_MBM_TOTAL_EVENT_ID;
>  
> +	if (r->mon.mbm_cntr_assignable)
> +		resctrl_file_fflags_init("num_mbm_cntrs", RFTYPE_MON_INFO);

Missing RFTYPE_RES_CACHE?

> +
>  	return 0;
>  }
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 626be6becca7..0c9d7a702b93 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -912,6 +912,30 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
>  	return 0;
>  }
>  
> +static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
> +				      struct seq_file *s, void *v)
> +{
> +	struct rdt_resource *r = of->kn->parent->priv;
> +	struct rdt_mon_domain *dom;
> +	bool sep = false;
> +
> +	cpus_read_lock();
> +	mutex_lock(&rdtgroup_mutex);
> +
> +	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
> +		if (sep)
> +			seq_puts(s, ";");

seq_putc() can be used.

> +
> +		seq_printf(s, "%d=%d", dom->hdr.id, r->mon.num_mbm_cntrs);
> +		sep = true;
> +	}
> +	seq_puts(s, "\n");

seq_putc() can be used.

> +
> +	mutex_unlock(&rdtgroup_mutex);
> +	cpus_read_unlock();
> +	return 0;
> +}
> +
>  #ifdef CONFIG_PROC_CPU_RESCTRL
>  
>  /*
> @@ -1945,6 +1969,12 @@ static struct rftype res_common_files[] = {
>  		.seq_show	= resctrl_mbm_assign_mode_show,
>  		.fflags		= RFTYPE_MON_INFO,
>  	},
> +	{
> +		.name		= "num_mbm_cntrs",
> +		.mode		= 0444,
> +		.kf_ops		= &rdtgroup_kf_single_ops,
> +		.seq_show	= resctrl_num_mbm_cntrs_show,
> +	},
>  	{
>  		.name		= "cpus",
>  		.mode		= 0644,

Reinette