linux-kernel - Re: [PATCH v1 30/31] x86/resctrl: Move the filesystem bits to headers visible to fs/resctrl

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Date: Mon, 15 Apr 2024 11:03:32 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Dave Martin <Dave.Martin@....com>
CC: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, 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>
Subject: Re: [PATCH v1 30/31] x86/resctrl: Move the filesystem bits to headers
 visible to fs/resctrl

Hi Dave,

On 4/12/2024 9:20 AM, Dave Martin wrote:
> On Thu, Apr 11, 2024 at 10:43:55AM -0700, Reinette Chatre wrote:
>> Hi Dave,
>>
>> On 4/11/2024 7:28 AM, Dave Martin wrote:
>>> On Mon, Apr 08, 2024 at 08:42:00PM -0700, Reinette Chatre wrote:
>>>> Hi James,
>>>>
>>>> On 3/21/2024 9:51 AM, James Morse wrote:
>>>> ..
>>>>> diff --git a/include/linux/resctrl_types.h b/include/linux/resctrl_types.h
>>>>> index 4788bd95dac6..fe0b10b589c0 100644
>>>>> --- a/include/linux/resctrl_types.h
>>>>> +++ b/include/linux/resctrl_types.h
>>>>> @@ -7,6 +7,36 @@
>>>>>  #ifndef __LINUX_RESCTRL_TYPES_H
>>>>>  #define __LINUX_RESCTRL_TYPES_H
>>>>>  
>>>>> +#define CQM_LIMBOCHECK_INTERVAL	1000
>>>>> +
>>>>> +#define MBM_CNTR_WIDTH_BASE		24
>>>>> +#define MBM_OVERFLOW_INTERVAL		1000
>>>>> +#define MAX_MBA_BW			100u
>>>>> +#define MBA_IS_LINEAR			0x4
>>>>> +
>>>>> +/* rdtgroup.flags */
>>>>> +#define	RDT_DELETED		1
>>>>> +
>>>>> +/* rftype.flags */
>>>>> +#define RFTYPE_FLAGS_CPUS_LIST	1
>>>>> +
>>>>> +/*
>>>>> + * Define the file type flags for base and info directories.
>>>>> + */
>>>>> +#define RFTYPE_INFO			BIT(0)
>>>>> +#define RFTYPE_BASE			BIT(1)
>>>>> +#define RFTYPE_CTRL			BIT(4)
>>>>> +#define RFTYPE_MON			BIT(5)
>>>>> +#define RFTYPE_TOP			BIT(6)
>>>>> +#define RFTYPE_RES_CACHE		BIT(8)
>>>>> +#define RFTYPE_RES_MB			BIT(9)
>>>>> +#define RFTYPE_DEBUG			BIT(10)
>>>>> +#define RFTYPE_CTRL_INFO		(RFTYPE_INFO | RFTYPE_CTRL)
>>>>> +#define RFTYPE_MON_INFO			(RFTYPE_INFO | RFTYPE_MON)
>>>>> +#define RFTYPE_TOP_INFO			(RFTYPE_INFO | RFTYPE_TOP)
>>>>> +#define RFTYPE_CTRL_BASE		(RFTYPE_BASE | RFTYPE_CTRL)
>>>>> +#define RFTYPE_MON_BASE			(RFTYPE_BASE | RFTYPE_MON)
>>>>> +
>>>>>  /* Reads to Local DRAM Memory */
>>>>>  #define READS_TO_LOCAL_MEM		BIT(0)
>>>>>  
>>>>
>>>> Not all these new seem to belong in this file. Could you please confirm?
>>>>
>>>> For example:
>>>> Earlier in series it was mentioned that struct rdtgroup is private to the
>>>> fs so having RDT_DELETED is unexpected as it implies access to struct rdtgroup.
>>>>
>>>> CQM_LIMBOCHECK_INTERVAL seems private to the fs code, so too
>>>> RFTYPE_FLAGS_CPUS_LIST.
>>>>
>>>> Reinette
>>>>
>>>
>>> I'll flag this for James to review.
>>>
>>> These have to be moved out of the x86 private headers, but you're right
>>> that some of them seem logically private to the resctrl core.
>>>
>>> I guess some of these could move to fs/resctrl/internal.h?
>>
>> It looks to me that way.
>>
>>>
>>> OTOH, might it be preferable to keep all the flag definitions for a
>>> given member together for ease of maintenance, even if some are for
>>> resctrl internal use only?
>>
>> Indeed, those RFTYPE flags really seem to be fs code but I agree that
>> architectures' use of RFTYPE_RES_CACHE and RFTYPE_RES_MB does make this
>> complicated and having these in a central place is reasonable to me.
>>
>> Reinette
> 
> Maybe we could split these into two groups, and clearly comment the ones
> that have no user outside resctrl as internal use only?

Another option to consider, which I think you hinted about earlier, is
to add an enum that maps to the RFTYPE_RES_CACHE and RFTYPE_RES_MB
flags. Just like, for example, RDTCTRL_GROUP maps to RFTYPE_CTRL.
The new enum can then be used similar to enum rdt_group_type to pick the
appropriate files based on RFTYPE_RES_CACHE or RFTYPE_RES_MB. 

> 
> That's not as clean as removing those definitions from a shared header,
> but at least would help document the issue until/unless a better
> solution is found...
> 
> Cheers
> ---Dave