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Date: Tue, 7 May 2024 11:28:20 -0500
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From: "Moger, Babu" <babu.moger@amd.com>
Subject: Re: [RFC PATCH v3 05/17] x86/resctrl: Introduce the interface to
 display the assignment state
Reply-To: babu.moger@amd.com
To: Reinette Chatre <reinette.chatre@intel.com>, corbet@lwn.net,
 fenghua.yu@intel.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
 dave.hansen@linux.intel.com
Cc: x86@kernel.org, hpa@zytor.com, paulmck@kernel.org, rdunlap@infradead.org,
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 rick.p.edgecombe@intel.com, kirill.shutemov@linux.intel.com,
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 ilpo.jarvinen@linux.intel.com, peternewman@google.com,
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Hi Reinette,

On 5/3/24 18:28, Reinette Chatre wrote:
> Hi Babu,
> 
> On 3/28/2024 6:06 PM, Babu Moger wrote:
>> The ABMC feature provides an option to the user to assign an RMID
>> to the hardware counter and monitor the bandwidth for a longer duration.
>> System can be in only one mode at a time (Legacy Monitor mode or ABMC
>> mode). By default, ABMC mode is disabled.
> 
> "By default, ABMC mode is disabled." seems to contradict later work.

Yes. Will correct it.

> 
>>
>> Provide an interface to display the monitor mode on the system.
>>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign
>>     abmc
> 
> This example seems to contradict earlier statements in two ways:
> (a) it only shows one mode vs. there are two modes (legacy or ABMC)
> (b) there is no active mode vs. one mode is always active.

I need to correct the commit messages. At this point this interface is
read-only. I will move some of this commit message to patch 15/17.

> 
>>
>> When the feature is enabled
>>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign
>>     [abmc]
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>> v3: New patch to display ABMC capability.
>> ---
>>  Documentation/arch/x86/resctrl.rst     |  5 +++++
>>  arch/x86/kernel/cpu/resctrl/monitor.c  |  4 +++-
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 17 +++++++++++++++++
>>  3 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 68df7751d1f5..cd973a013525 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -257,6 +257,11 @@ 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":
>> +	Available when assignable monitoring features are supported.
>> +	Reports the list of assignable features supported and the enclosed brackets
>> +	indicate the feature is enabled.
> 
> "indicate the feature is enabled" -> "indicate which feature is enabled" or
> "indicates the currently enabled feature" or ...?

This looks good.

> 
>> +
>>  "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 735b449039c1..48d1957ea5a3 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1058,8 +1058,10 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>>  						 RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
>>  		}
>>  
>> -		if (resctrl_arch_has_abmc(r))
>> +		if (resctrl_arch_has_abmc(r)) {
>>  			r->mbm_assign_capable = ABMC_ASSIGN;
>> +			resctrl_file_fflags_init("mbm_assign", RFTYPE_MON_INFO);
> 
> I think this will need some more thought when considering the fs/arch split.
> The architecture can be expected to set r->mbm_assign_capable as above but
> having the architecture meddle with the fs flags does not seem like the right
> thing to do. I think that RFTYPE_MON_INFO may not be accessible to arch code
> anyway.

It is accessible to both arch and fs code per latest code.
https://lore.kernel.org/lkml/20240426150904.8854-33-Dave.Martin@arm.com/

> 
>> +		}
>>  	}
>>  
>>  	l3_mon_evt_init(r);
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index dda71fb6c10e..5ec807e8dd38 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -846,6 +846,17 @@ static int rdtgroup_rmid_show(struct kernfs_open_file *of,
>>  	return ret;
>>  }
>>  
>> +static int rdtgroup_mbm_assign_show(struct kernfs_open_file *of,
>> +				    struct seq_file *s, void *v)
>> +{
>> +	struct rdt_resource *r = of->kn->parent->priv;
>> +
>> +	if (r->mbm_assign_capable)
>> +		seq_puts(s, "abmc\n");
>> +
>> +	return 0;
>> +}
> 
> Should it print "legacy" if not mbm_assign_capable? Or actually, I think
> the expectation is that this file will only be accessible if 
> r->mbm_assign_capable is true ... so having that if (r->mbm_assign_capable)

Correct. I need to move code from patch 7/17 here to correct this.


> check is not clear to me ... if that is false then it would be a kernel
> bug, no?

Yes. This is not correct. I need to fix this.

> 
>> +
>>  #ifdef CONFIG_PROC_CPU_RESCTRL
>>  
>>  /*
>> @@ -1903,6 +1914,12 @@ static struct rftype res_common_files[] = {
>>  		.seq_show	= mbm_local_bytes_config_show,
>>  		.write		= mbm_local_bytes_config_write,
>>  	},
>> +	{
>> +		.name		= "mbm_assign",
>> +		.mode		= 0444,
>> +		.kf_ops		= &rdtgroup_kf_single_ops,
>> +		.seq_show	= rdtgroup_mbm_assign_show,
>> +	},
>>  	{
>>  		.name		= "cpus",
>>  		.mode		= 0644,
> 
> Reinette
> 

-- 
Thanks
Babu Moger