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

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Message-ID: <811b0f54-4c59-43fd-a551-3485b242e20d@amd.com>
Date: Fri, 7 Feb 2025 12:59:55 -0600
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 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 Reinette,

On 2/5/2025 6:19 PM, Reinette Chatre wrote:
> 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"?

Sure.

> 
>>
>> 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:"

Sure.

> 
> 
>> +	 # 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()?

Yes.

> 
>> +	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().

Sure.
     seq_putc(s, ';');

> 
>> +
>> +		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?

Sure.

> 
>> +		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
> 

Thanks
Babu