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

[Ben Horgan <ben.horgan@arm.com>]

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.

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.

Thanks,

Ben

> 
>>
>> before the final sentence to make it clear that this change is an improvement not just
>> a change in policy.
> 
> Reinette