Re: [PATCH v6 12/42] x86/resctrl: Move rdt_find_domain() to be visible to arch and fs code

[Reinette Chatre]

Hi Catalin,

On 2/20/25 2:58 AM, Catalin Marinas wrote:
> On Wed, Feb 19, 2025 at 03:24:06PM -0800, Reinette Chatre wrote:
>> On 2/7/25 10:17 AM, James Morse wrote:
>>> rdt_find_domain() finds a domain given a resource and a cache-id.
>>> This is used by both the architecture code and the filesystem code.
>>>
>>> After the filesystem code moves to live in /fs/, this helper will no
>>> longer be visible.
>>>
>>> Move it to the global header file. As its now globally visible, and
>>> has only a handful of callers, swap the 'rdt' for 'resctrl'.
> [...]
>>> --- a/include/linux/resctrl.h
>>> +++ b/include/linux/resctrl.h
>>> @@ -372,6 +372,40 @@ static inline void resctrl_arch_rmid_read_context_check(void)
>>>  		might_sleep();
>>>  }
>>>  
>>> +/**
>>> + * resctrl_find_domain() - Search for a domain id in a resource domain list.
>>> + * @h:		The domain list to search.
>>> + * @id:		The domain id to search for.
>>> + * @pos:	A pointer to position in the list id should be inserted.
>>> + *
>>> + * Search the domain list to find the domain id. If the domain id is
>>> + * found, return the domain. NULL otherwise.  If the domain id is not
>>> + * found (and NULL returned) then the first domain with id bigger than
>>> + * the input id can be returned to the caller via @pos.
>>> + */
>>> +static inline struct rdt_domain_hdr *resctrl_find_domain(struct list_head *h,
>>> +							 int id,
>>> +							 struct list_head **pos)
>>
>> Could you please provide a motivation for why this needs to be inline now?
> 
> It's in a header now, to avoid the compiler complaining about unused
> static functions wherever this file is included. The alternative is a
> prototype declaration and the actual implementation in a .c file.

resctrl_find_domain() is currently in a .c file (arch/x86/kernel/cpu/resctrl/core.c)
with a prototype declaration (in arch/x86/kernel/cpu/resctrl/internal.h). This patch
switches resctrl_find_domain() to be inline without a motivation.

After a fresh reading of "The inline disease" in Documentation/process/coding-style.rst 
I do see a few red flags related to making this function inline. The function is certainly
larger than the rule of thumb of "3 lines" and considering the number of call sites I do
not see how bloating the kernel is justified.

> 
> (drive-by comment, I don't really understand this subsystem to make a
> meaningful contribution)
> 

Thanks for taking a look. The idea is not unique to resctrl.

Reinette