Re: [PATCH v4 5/7] fs/resctrl: Continue counter allocation after failure

[Reinette Chatre]

Hi Ben,

On 4/15/26 7:46 AM, Ben Horgan wrote:
> Hi Reinette,
> 
> On 4/15/26 15:27, Reinette Chatre wrote:
>> Hi Ben,
>>
>> On 4/14/26 7:42 AM, Ben Horgan wrote:
>>> On 3/27/26 16:21, Reinette Chatre wrote:
>>
>>>> Consider a changelog like below that just focuses on problem being solved
>>>> (but please correct me if you find I am missing the point):
>>>>
>>>> 	In mbm_event mode, with mbm_assign_on_mkdir set to 1, when a user
>>>> 	creates a new CTRL_MON or MON group resctrl attempts to allocate
>>>> 	counters for each of the supported MBM events on each resctrl
>>>> 	domain. As counters are limited, such allocation may fail and
>>>> 	when it does counter allocations for the remaining domains are
>>>> 	skipped even if the domains have available counters.                                                                       
>>>>                                                                                 
>>>> 	Since a counter allocation failure may result in counter allocation
>>>> 	skipped on other domains the user needs to view the resource group's
>>>
>>> skipped -> being skipped
>>>
>>>> 	mbm_L3_assignments files to get an accurate view of counter assignment
>>>> 	in a new resource group and then manually create counters in the skipped
>>>> 	domains	with available counters.                                             
>>>>                                                                                 
>>>> 	Writes to mbm_L3_assignments using the wildcard format, <event>:*=e,            
>>>> 	also skip counter allocation in other domains after a counter allocation      
>>>> 	failure.                                                                        
>>>>                                                                                 
>>>> 	When handling a request to create counters in all domains it is unnecessary
>>>> 	for a counter allocation in one domain to prevent counter allocation in
>>>> 	other domains. Always attempt to allocate all the counters requested.     
>>>
>>> I can use this but how about if I add,
>>>
>>> Skipping counter allocation in subsequent domains after failure makes predicting which
>>> counters will be allocated harder for the user as they need to know the ordering of the
>>> domains as well as the expected failures.
>>
>> I do not see why the user needs to make any predictions with the current implementation.
>> mbm_L3_assignments will always contain accurate information regarding counter assignment, no?
> 
> They can see the result with mbm_L3_assignments. In general, if the user is doing any operation it helps for them to
> know what they can expect from that operation before doing it.

I totally agree. I seem to be missing the goal here. Are you saying that currently it is not clear
what the user can expect when running these commands? I believe that is clarified with the documentation
update in patch #6? 

> 
> Happy to drop the extra sentence if you don't think it adds anything. Making all allocations of multiple counters best
> effort is the main point.

I do not object adding extra sentences but the proposal mentions how user space needs to
predict behaviors and know about kernel internals which I do not believe is required now nor
with planned changes. I really seem to be missing something here so would appreciate if you
could elaborate the goals here.

Reinette