linux-kernel - Re: [PATCH v10 20/24] x86/resctrl: Introduce the interface to switch between monitor modes

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Message-ID: <156e6bb5-650d-427c-8750-28b2d03cd587@amd.com>
Date: Sat, 21 Dec 2024 08:20:30 -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: fenghua.yu@...el.com, 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 v10 20/24] x86/resctrl: Introduce the interface to switch
 between monitor modes

Hi Reinette,

On 12/19/2024 8:56 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 12/12/24 12:15 PM, Babu Moger wrote:
>> Introduce interface to switch between mbm_cntr_assign and default modes.
>>
> 
> This changelog needs context.

Sure.

> 
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> [mbm_cntr_assign]
>> default
>>
>> To enable the "mbm_cntr_assign" mode:
>> $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> To enable the default monitoring mode:
>> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> MBM event counters will reset when mbm_assign_mode is changed.
> 
> I think it will help to elaborate on this.
> 
> I understand this as two parts. As stated, the hardware counters
> are reset since that is what ABMC does. In this patch
> there is a mbm_cntr_reset() but that does not actually reset the counters as
> the above implies.
> Instead, the counters are automatically reset as part of changing the mode.
> resctrl triggers reset of architectural and non-architectural
> state of the events because of the hardware counter reset.
> 
> The changelog can really do more to explain what this patch does.

Ok. Will do.

> 
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
>> ---
>>   Documentation/arch/x86/resctrl.rst     | 15 ++++++++
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 50 +++++++++++++++++++++++++-
>>   2 files changed, 64 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 3ec14c314606..d3a8a34cf629 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -290,6 +290,21 @@ with the following files:
>>   	"mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if
>>   	there is no counter associated with that event.
>>   
>> +	* To enable "mbm_cntr_assign" mode:
>> +	  ::
>> +
>> +	    # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> +	* To enable default monitoring mode:
>> +	  ::
>> +
>> +	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> +	The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated with
>> +	counters may reset when "mbm_assign_mode" is changed. Moving to
> 
> After looking at the final documentation it seems more appropriate to move this to
> the top of the "mbm_assign_mode" section. The top already shows how to read from the
> file using cat so it seems like a good match to document write to the file in the
> same area.

ok.

> 
>> +	mbm_cntr_assign mode require users to assign the counters to the events.
>> +	Otherwise, the MBM event counters will return "Unassigned" when read.
> 
> This portion can move to the mode it applies to.

ok.

> 
>> +
>>   "num_mbm_cntrs":
>>   	The number of monitoring counters available for assignment when the
>>   	architecture supports mbm_cntr_assign mode.
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 8d00b1689a80..eea534cce3d0 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -939,6 +939,53 @@ static void mbm_cntr_reset(struct rdt_resource *r)
>>   	}
>>   }
>>   
>> +static ssize_t rdtgroup_mbm_assign_mode_write(struct kernfs_open_file *of,
>> +					      char *buf, size_t nbytes, loff_t off)
> 
> rdtgroup_ namespace is not appropriate

Will rename as resctrl_

thanks
Babu