linux-kernel - Re: [PATCH v11 07/23] x86/resctrl: Introduce the interface to display monitor mode

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Message-ID: <7b1765c8-9944-44db-9a0b-fddd102f156b@amd.com>
Date: Thu, 6 Feb 2025 17:41:59 -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 07/23] x86/resctrl: Introduce the interface to display
 monitor mode

Hi Reinette,

On 2/6/2025 12:01 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 1/22/25 12:20 PM, Babu Moger wrote:
>> Introduce the interface file "mbm_assign_mode" to list monitor modes
>> supported.
>>
>> The "mbm_cntr_assign" mode provides the option to assign a counter to
>> an RMID, event pair and monitor the bandwidth as long as it is assigned.
>>
>> On AMD systems "mbm_cntr_assign" is backed by the ABMC (Assignable
> 
> ""mbm_cntr_assign" is backed" -> ""mbm_cntr_assign" mode is backed"?

Sure.
> 
>> Bandwidth Monitoring Counters) hardware feature and is enabled by default.
>>
>> The "default" mode is the existing monitoring mode that works without the
>> explicit counter assignment, instead relying on dynamic counter assignment
>> by hardware that may result in hardware not dedicating a counter resulting
>> in monitoring data reads returning "Unavailable".
>>
>> Provide an interface to display the monitor mode on the system.
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> [mbm_cntr_assign]
>> default
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> 
>> ---
>>   Documentation/arch/x86/resctrl.rst     | 26 +++++++++++++++++++++
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 31 ++++++++++++++++++++++++++
>>   2 files changed, 57 insertions(+)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index fb90f08e564e..b5defc5bce0e 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -257,6 +257,32 @@ 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_mode":
>> +	Reports the list of monitoring modes supported. The enclosed brackets
>> +	indicate which mode is enabled.
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +	  [mbm_cntr_assign]
>> +	  default
>> +
>> +	"mbm_cntr_assign":
>> +
>> +	In mbm_cntr_assign, monitoring event can only accumulate data while
> 
> "In mbm_cntr_assign, monitoring event" -> "In mbm_cntr_assign mode, a monitoring event"?

Sure.

> 
>> +	it is backed by a hardware counter. The user-space is able to specify
>> +	which of the events in CTRL_MON or MON groups should have a counter
>> +	assigned using the "mbm_assign_control" file. The number of counters
>> +	available is described in the "num_mbm_cntrs" file. Changing the mode
>> +	may cause all counters on a resource to reset.
>> +
>> +	"default":
>> +
>> +	In default mode, resctrl assumes there is a hardware counter for each
>> +	event within every CTRL_MON and MON group. On AMD platforms, it is
>> +	recommended to use mbm_cntr_assign mode if supported, because reading
>> +	"mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if
> 
> Reinette
> 

Thanks
Babu