linux-kernel - Re: [PATCH v11 12/23] x86/resctrl: Introduce interface to display number of free counters

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Message-ID: <bc963e40-46cd-42a2-95f0-a2e1a35cbc25@intel.com>
Date: Wed, 5 Feb 2025 16:19:28 -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 12/23] x86/resctrl: Introduce interface to display
 number of free counters

Hi Babu,

On 1/22/25 12:20 PM, Babu Moger wrote:
> Provide the interface to display the number of monitoring counters
> available for assignment in each domain when mbm_cntr_assign is enabled.

"when mbm_cntr_assign is enabled" -> "when mbm_cntr_assign mode is enabled"?

> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---


> ---
>  Documentation/arch/x86/resctrl.rst     |  8 +++++
>  arch/x86/kernel/cpu/resctrl/monitor.c  |  1 +
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 46 ++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+)
> 
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index 31ff764deeeb..99cae75559b0 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -299,6 +299,14 @@ with the following files:
>  	memory bandwidth tracking to a single memory bandwidth event per
>  	monitoring group.
>  
> +"available_mbm_cntrs":
> +	The number of monitoring counters available for assignment in each
> +	domain when mbm_cntr_assign mode is enabled on the system.
> +	::
> +

Documentation jumps in with some hardcoded values that may cause confusion.
It looks to be missing something like (and looking back this also applies
to "num_mbm_cntrs"):
"For example, on a system with 30 available monitoring/(hardware?) counters in
each of its L3 domains:"


> +	 # cat /sys/fs/resctrl/info/L3_MON/available_mbm_cntrs
> +	 0=30;1=30
> +


>  "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 6fe9e610e9a0..f2bf5b13465d 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -1234,6 +1234,7 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>  			cpuid_count(0x80000020, 5, &eax, &ebx, &ecx, &edx);
>  			r->mon.num_mbm_cntrs = (ebx & GENMASK(15, 0)) + 1;
>  			resctrl_file_fflags_init("num_mbm_cntrs", RFTYPE_MON_INFO);
> +			resctrl_file_fflags_init("available_mbm_cntrs", RFTYPE_MON_INFO);
>  		}
>  	}
>  
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 75a3b56996ca..2b86124c336b 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -888,6 +888,46 @@ static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
>  	return 0;
>  }
>  
> +static int resctrl_available_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;
> +	u32 cntrs, i;
> +	int ret = 0;
> +
> +	cpus_read_lock();
> +	mutex_lock(&rdtgroup_mutex);
> +

Missing rdt_last_cmd_clear()?

> +	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
> +		rdt_last_cmd_puts("mbm_cntr_assign mode is not enabled\n");
> +		ret = -EINVAL;
> +		goto unlock_cntrs_show;
> +	}
> +
> +	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
> +		if (sep)
> +			seq_puts(s, ";");

The one character prints can be simplified with a seq_putc().

> +
> +		cntrs = 0;
> +		for (i = 0; i < r->mon.num_mbm_cntrs; i++) {
> +			if (!dom->cntr_cfg[i].rdtgrp)
> +				cntrs++;
> +		}
> +
> +		seq_printf(s, "%d=%d", dom->hdr.id, cntrs);

I expect cntrs to need %u?

> +		sep = true;
> +	}
> +	seq_puts(s, "\n");
> +
> +unlock_cntrs_show:
> +	mutex_unlock(&rdtgroup_mutex);
> +	cpus_read_unlock();
> +
> +	return ret;
> +}
> +
>  #ifdef CONFIG_PROC_CPU_RESCTRL
>  
>  /*
> @@ -1916,6 +1956,12 @@ static struct rftype res_common_files[] = {
>  		.kf_ops		= &rdtgroup_kf_single_ops,
>  		.seq_show	= resctrl_num_mbm_cntrs_show,
>  	},
> +	{
> +		.name		= "available_mbm_cntrs",
> +		.mode		= 0444,
> +		.kf_ops		= &rdtgroup_kf_single_ops,
> +		.seq_show	= resctrl_available_mbm_cntrs_show,
> +	},
>  	{
>  		.name		= "cpus",
>  		.mode		= 0644,

Reinette