linux-kernel - Re: [RFC PATCH v3 03/17] x86/resctrl: Detect Assignable Bandwidth Monitoring feature details

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Date: Thu, 9 May 2024 20:18:00 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....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>,
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	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [RFC PATCH v3 03/17] x86/resctrl: Detect Assignable Bandwidth
 Monitoring feature details

Hi Babu,

On 5/9/2024 3:34 PM, Moger, Babu wrote:
> Hi Reinette,
> 
> On 5/7/24 15:27, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 5/6/2024 12:09 PM, Moger, Babu wrote:
>>> On 5/3/24 18:26, Reinette Chatre wrote:
>>>> On 3/28/2024 6:06 PM, Babu Moger wrote:
>>
>> ...
>>
>>>>> + * @mbm_assign_cntrs:	Maximum number of assignable counters
>>>>>   */
>>>>>  struct rdt_resource {
>>>>>  	int			rid;
>>>>> @@ -188,6 +198,8 @@ struct rdt_resource {
>>>>>  	struct list_head	evt_list;
>>>>>  	unsigned long		fflags;
>>>>>  	bool			cdp_capable;
>>>>> +	bool			mbm_assign_capable;
>>>>> +	u32                     mbm_assign_cntrs;
>>>>>  };
>>>>
>>>> Please check tabs vs spaces (in this whole series please).
>>>
>>> Sure. Will do.
>>>
>>>>
>>>> I'm thinking that a new "MBM specific" struct within
>>>> struct rdt_resource will be helpful to clearly separate the MBM related
>>>> data. This will be similar to struct resctrl_cache for 
>>>> cache allocation and struct resctrl_membw for memory bandwidth
>>>> allocation.
>>>
>>> Did you mean to move all the fields for monitoring to move to new struct?
>>>
>>> Struct resctrl_mbm {
>>>           int                     num_rmid;
>>>           bool                    mbm_assign_capable;
>>>           u32                     mbm_assign_cntrs;
>>> }:
>>>
>>
>> Indeed, so not actually MBM specific but monitoring specific as you state (with
>> appropriate naming?). This is purely to help organize data within struct rdt_resource
>> and (similar to struct resctrl_cache and struct resctrl_membw) not a new
>> structure expected to be passed around. I think evt_list can also be a member.
> 
> How about this?
> 
> Lets keep assign_capable in main structure(like we have mon_capable) and
> move rest of them into new structure.
> 
> Struct resctrl_mon {
>            int                     num_rmid;
> 	   struct list_head        evt_list;
>            u32                     num_assign_cntrs;
> }:

This looks like a good start. It certainly supports ABMC. I do not yet
have a clear understanding about how this will support MPAM and soft-RMID/ABMC
since the current implementation has an implicit scope of one counter per event per
monitor group. It thus seem reasonable to have a new generic name of "cntrs".

Reinette