Message-ID: <c531c218-6eee-4262-a89f-50e1bfde6dfb@amd.com>
Date: Mon, 10 Feb 2025 13:46:57 -0600
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.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 23/23] x86/resctrl: Introduce interface to modify
 assignment states of the groups

Hi Reinette,

On 2/6/25 12:48, Reinette Chatre wrote:
> Hi Babu,
> 
> On 1/22/25 12:20 PM, Babu Moger wrote:
>> When mbm_cntr_assign mode is enabled, users can designate which of the MBM
>> events in the CTRL_MON or MON groups should have counters assigned.
>>
>> Provide an interface for assigning MBM events by writing to the file:
>> /sys/fs/resctrl/info/L3_MON/mbm_assign_control. Using this interface,
>> events can be assigned or unassigned as needed.
>>
>> Format is similar to the list format with addition of opcode for the
>> assignment operation.
>>  "<CTRL_MON group>/<MON group>/<domain_id><opcode><flags>"
>>
>> Format for specific type of groups:
>>
>>  * Default CTRL_MON group:
>>          "//<domain_id><opcode><flags>"
>>
>>  * Non-default CTRL_MON group:
>>          "<CTRL_MON group>//<domain_id><opcode><flags>"
>>
>>  * Child MON group of default CTRL_MON group:
>>          "/<MON group>/<domain_id><opcode><flags>"
>>
>>  * Child MON group of non-default CTRL_MON group:
>>          "<CTRL_MON group>/<MON group>/<domain_id><opcode><flags>"
>>
>> Domain_id '*' will apply the flags on all the domains.
>>
>> Opcode can be one of the following:
>>
>>  = Update the assignment to match the flags
>>  + Assign a new MBM event without impacting existing assignments.
>>  - Unassign a MBM event from currently assigned events.
>>
>> Assignment flags can be one of the following:
>>  t  MBM total event
>>  l  MBM local event
>>  tl Both total and local MBM events
>>  _  None of the MBM events. Valid only with '=' opcode. This flag cannot
>>     be combined with other flags.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v11: Fixed the static check warning with initializing dom_id in resctrl_process_flags().
>>
>> v10: Fixed the issue with finding the domain in multiple iterations.
>>      Printed error message with domain information when assign fails.
>>      Changed the variables to unsigned for processing assign state.
>>      Taken care of few format corrections.
>>
>> v9: Fixed handling special case '//0=' and '//".
>>     Removed extra strstr() call.
>>     Added generic failure text when assignment operation fails.
>>     Corrected user documentation format texts.
>>
>> v8: Moved unassign as the first action during the assign modification.
>>     Assign none "_" takes priority. Cannot be mixed with other flags.
>>     Updated the documentation and .rst file format. htmldoc looks ok.
>>
>> v7: Simplified the parsing (strsep(&token, "//") in rdtgroup_mbm_assign_control_write().
>>     Added mutex lock in rdtgroup_mbm_assign_control_write() while processing.
>>     Renamed rdtgroup_find_grp to rdtgroup_find_grp_by_name.
>>     Fixed rdtgroup_str_to_mon_state to return error for invalid flags.
>>     Simplified the calls rdtgroup_assign_cntr by merging few functions earlier.
>>     Removed ABMC reference in FS code.
>>     Reinette commented about handling the combination of flags like 'lt_' and '_lt'.
>>     Not sure if we need to change the behaviour here. Processed them sequencially right now.
>>     Users have the liberty to pass the flags. Restricting it might be a problem later.
>>
>> v6: Added support assign all if domain id is '*'
>>     Fixed the allocation of counter id if it not assigned already.
>>
>> v5: Interface name changed from mbm_assign_control to mbm_control.
>>     Fixed opcode and flags combination.
>>     '=_" is valid.
>>     "-_" amd "+_" is not valid.
>>     Minor message update.
>>     Renamed the function with prefix - rdtgroup_.
>>     Corrected few documentation mistakes.
>>     Rebase related changes after SNC support.
>>
>> v4: Added domain specific assignments. Fixed the opcode parsing.
>>
>> v3: New patch.
>>     Addresses the feedback to provide the global assignment interface.
>> ---
>>  Documentation/arch/x86/resctrl.rst     | 116 +++++++++++-
>>  arch/x86/kernel/cpu/resctrl/internal.h |  10 +
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 241 ++++++++++++++++++++++++-
>>  3 files changed, 365 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 3040e5c4cd76..47e15b48d951 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -356,7 +356,8 @@ with the following files:
>>  	 t  MBM total event is assigned.
>>  	 l  MBM local event is assigned.
>>  	 tl Both MBM total and local events are assigned.
>> -	 _  None of the MBM events are assigned.
>> +	 _  None of the MBM events are assigned. Only works with opcode '=' for write
>> +	    and cannot be combined with other flags.
>>  
>>  	Examples:
>>  	::
>> @@ -374,6 +375,119 @@ with the following files:
>>  	There are four resctrl groups. All the groups have total and local MBM events
>>  	assigned on domain 0 and 1.
>>  
>> +	Assignment state can be updated by writing to "mbm_assign_control".
>> +
>> +	Format is similar to the list format with addition of opcode for the
>> +	assignment operation.
>> +
>> +		"<CTRL_MON group>/<MON group>/<domain_id><opcode><flags>"
>> +
>> +	Format for each type of group:
>> +
>> +        * Default CTRL_MON group:
>> +                "//<domain_id><opcode><flags>"
>> +
>> +        * Non-default CTRL_MON group:
>> +                "<CTRL_MON group>//<domain_id><opcode><flags>"
>> +
>> +        * Child MON group of default CTRL_MON group:
>> +                "/<MON group>/<domain_id><opcode><flags>"
>> +
>> +        * Child MON group of non-default CTRL_MON group:
>> +                "<CTRL_MON group>/<MON group>/<domain_id><opcode><flags>"
>> +
>> +	Domain_id '*' will apply the flags to all the domains.
>> +
>> +	Opcode can be one of the following:
>> +	::
>> +
>> +	 = Update the assignment to match the MBM event.
>> +	 + Assign a new MBM event without impacting existing assignments.
>> +	 - Unassign a MBM event from currently assigned events.
>> +
>> +	Examples:
>> +	Initial group status:
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +	  non_default_ctrl_mon_grp//0=tl;1=tl
>> +	  non_default_ctrl_mon_grp/child_non_default_mon_grp/0=tl;1=tl
>> +	  //0=tl;1=tl
>> +	  /child_default_mon_grp/0=tl;1=tl
>> +
>> +	To update the default group to assign only total MBM event on domain 0:
>> +	::
>> +
>> +	  # echo "//0=t" > /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +
>> +	Assignment status after the update:
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +	  non_default_ctrl_mon_grp//0=tl;1=tl
>> +	  non_default_ctrl_mon_grp/child_non_default_mon_grp/0=tl;1=tl
>> +	  //0=t;1=tl
>> +	  /child_default_mon_grp/0=tl;1=tl
>> +
>> +	To update the MON group child_default_mon_grp to remove total MBM event on domain 1:
>> +	::
>> +
>> +	  # echo "/child_default_mon_grp/1-t" > /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +
>> +	Assignment status after the update:
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +	  non_default_ctrl_mon_grp//0=tl;1=tl
>> +	  non_default_ctrl_mon_grp/child_non_default_mon_grp/0=tl;1=tl
>> +	  //0=t;1=tl
>> +	  /child_default_mon_grp/0=tl;1=l
>> +
>> +	To update the MON group non_default_ctrl_mon_grp/child_non_default_mon_grp to unassign
>> +	both local and total MBM events on domain 1:
>> +	::
>> +
>> +	  # echo "non_default_ctrl_mon_grp/child_non_default_mon_grp/1=_" >
>> +			/sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +
>> +	Assignment status after the update:
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> +	  non_default_ctrl_mon_grp//0=tl;1=tl
>> +	  non_default_ctrl_mon_grp/child_non_default_mon_grp/0=tl;1=_
>> +	  //0=t;1=tl
>> +	  /child_default_mon_grp/0=tl;1=l
>> +
>> +	To update the default group to add a local MBM event domain 0:
> 
> "local MBM event domain 0" -> "local MBM event on domain 0"?

Sure.

> 
> Taking a step back to look at the completed "mbm_assign_control" section
> it is noteworthy that all this work is about assigning counters to events
> but after this large section is complete the word "counter" does not appear
> a single time.
> 
> The section starts with a brief:
> "Reports the resctrl group and monitor status of each group." and then
> moves to terms like "assigning events"/"assignment status" without defining
> what that means.
> 
> Instead of rewriting this, what do you think of adding some definition
> of what "assignment state" means to the start of the section. For example,
> (I am sure it can be improved):
> 
> "Use "mbm_assign_control" to manage monitoring counter assignment to
> monitoring events when mbm_cntr_assign_mode is enabled."


Sure.

-- 
Thanks
Babu Moger

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