linux-kernel - Re: [PATCH v5 21/40] x86/resctrl: Change mon_event_config

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Message-ID: <cb82676d-807b-42b9-b692-62adba91a063@arm.com>
Date: Fri, 7 Feb 2025 15:45:19 +0000
From: James Morse <james.morse@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
 shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>, Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v5 21/40] x86/resctrl: Change
 mon_event_config_{read,write}() to be arch helpers

Hi Reinette,

On 23/10/2024 23:19, Reinette Chatre wrote:
> On 10/4/24 11:03 AM, James Morse wrote:
>> @@ -315,6 +322,24 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
>>  
>>  bool __init resctrl_arch_is_evt_configurable(enum resctrl_event_id evt);
>>  
>> +/**
>> + * resctrl_arch_mon_event_config_write() - Write the config for a counter.
> 
> Please avoid the term "counter" for events ... the upcoming AMD work adds support
> for counters*. 

Fixed.


>> + * @info:	struct resctrl_mon_config_info describing the resource, domain
>> + *		and event.
> 
> Expected "config" to appear as part of information about function
> that claims to writes config?

I'll rename the variable.


>> + *
>> + * Must be called on a CPU that is a member of the specified domain.

> I am not sure about this. Is this documentation intended to support authors of
> arch code? In that case it may be instead useful to know that this function will be
> called on a CPU that is a member of the specified domain to avoid confusion from arch
> side whether it needs to take some action to ensure function is called on right CPU.
> 
> 	Called on a CPU that is a member of the specified domain.

I don't think we have clear idea who this documentation is for - I'm assuming its for the
caller...

I'll change this to "Called via IPI to reach a CPU that is a member of the specified
domain", as that covers both views, and adds that its called in irq context.


>> + */
>> +void resctrl_arch_mon_event_config_write(void *info);
>> +
>> +/**
>> + * resctrl_arch_mon_event_config_read() - Read the config for a counter.
> 
> counter -> event
> 
>> + * @info:	struct resctrl_mon_config_info describing the resource, domain
>> + *		and event.
> 
> Copy&paste? No information on how config is returned.

Laziness - there is only one possible place it could be! I've added:
| * Reads resource, domain and eventid from @config_info and reads the
|  * hardware config value into config_info->mon_config.

and similar on the other function.


Thanks,

James