linux-kernel - Re: [PATCH v6 08/22] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <807d4e97-67e1-4644-ab99-caccd328eb62@amd.com>
Date: Tue, 20 Aug 2024 10:56:04 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 fenghua.yu@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
 tj@...nel.org, peterz@...radead.org, yanjiewtw@...il.com,
 kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
 jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
 rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
 jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v6 08/22] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Reinette,

On 8/16/24 16:34, Reinette Chatre wrote:
> Hi Babu,
> 
> On 8/6/24 3:00 PM, Babu Moger wrote:
>> The ABMC feature provides an option to the user to assign a hardware
> 
> Here and in all patches, when referring to resctrl fs please use the more
> generic "mbm_assign_cntr" mode to distinguish it from the
> hardware/architecture
> specific code that involves ABMC. Something like
> 
> "The ABMC feature provides" -> ""mbm_cntr_assign" mode provides"

Sure.

> 
> I also think that being explicit with this separation will help us to see
> gaps in interface between resctrl fs and arch.

Yes.
> 
>> counter to an RMID and monitor the bandwidth as long as the counter is
> 
> Please clarify the scope of this feature. Above mentions that a counter is
> assigned to an RMID but later it is mentioned that the counter is assigned
> to an event. Perhaps consistently mention that a counter is assigned to
> a RMID,event pair?

Yes.
"a counter is assigned to an RMID,event pair" gives more clarity.
Will changes it.

> 
>> assigned. Number of assignments depend on number of monitoring counters
>> available.
>>
>> Provide the interface to display the number of monitoring counters
>> supported.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v6: No changes.
>>
>> v5: Changed the display name from num_cntrs to num_mbm_cntrs.
>>      Updated the commit message.
>>      Moved the patch after mbm_mode is introduced.
>>
>> v4: Changed the counter name to num_cntrs. And few text changes.
>>
>> v3: Changed the field name to mbm_assign_cntrs.
>>
>> v2: Changed the field name to mbm_assignable_counters from abmc_counte
>> ---
>>   Documentation/arch/x86/resctrl.rst     |  3 +++
>>   arch/x86/kernel/cpu/resctrl/monitor.c  |  2 ++
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 16 ++++++++++++++++
>>   3 files changed, 21 insertions(+)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst
>> b/Documentation/arch/x86/resctrl.rst
>> index d4ec605b200a..fe9f10766c4f 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -291,6 +291,9 @@ with the following files:
>>           as long as there are enough RMID counters available to support
>> number
>>           of monitoring groups.
>>   +"num_mbm_cntrs":
>> +    The number of monitoring counters available for assignment.
>> +
>>   "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 5e8706ab6361..83329cefebf7 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1242,6 +1242,8 @@ int __init rdt_get_mon_l3_config(struct
>> rdt_resource *r)
>>               r->mon.num_mbm_cntrs = (ebx & 0xFFFF) + 1;
>>               if (WARN_ON(r->mon.num_mbm_cntrs > 64))
>>                   r->mon.num_mbm_cntrs = 64;
>> +
>> +            resctrl_file_fflags_init("num_mbm_cntrs", RFTYPE_MON_INFO);
> 
> The arch code should not access the resctrl file flags. This should be
> moved to make
> the MPAM support easier. With the arch code setting
> r->mon.mbm_cntr_assignable the
> fs code can use that to set the flags. Something similar to below patch is
> needed:
> https://lore.kernel.org/lkml/20240802172853.22529-27-james.morse@arm.com/

It is just moving the calls resctrl_file_fflags_init() to resctrl_init().
The  rdt_resource fields are already setup here. Something like
https://lore.kernel.org/lkml/20240802172853.22529-20-james.morse@arm.com/

I feel it is better done when MBAM fs/arch separation.
-- 
Thanks
Babu Moger