Re: [PATCH v4] fs/resctrl: Add CONFIG_RESCTRL_ASSIGN_FIXED Kconfig entry

[Ben Horgan]

Hi Boris,

On 3/1/26 10:49, Borislav Petkov wrote:
> On Wed, Feb 04, 2026 at 04:19:52PM +0000, Ben Horgan wrote:
>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>> index 572a9925bd6c..4e9f55ee3267 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -1451,6 +1451,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
>>  	}
>>  
>>  	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>> +		if (IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
> 
> Does it need to be a Kconfig entry or you can figure out programatically from
> the architecture that that is the case and avoid yet another CONFIG_ knob?
> 
> From reading this, I'm thinking
> 
> 		if (IS ARM64) {
> 
> should do or...?

Yes, we don't necessarily need the Kconfig and we don't necessarily need this condition at all in
resctrl_mbm_assign_mode_write(), we do need the existing one in resctrl_mbm_assign_mode_show() though.

The Kconfig was effectively added in:

commit 3b497c3f4f04 ("fs/resctrl: Introduce the interface to display monitoring modes")

and I was just filling in the missing piece. Most arch specific things in resctrl seem
to be dealt with using resctrl_arch_* hooks. Would it be preferable to create a new one of these?
It could be resctrl_arch_mbm_cntr_assign_fixed() although we seem to be getting too many
of these too. Perhaps we could extend the meaning of another hook, resctrl_arch_mbm_assign_set() could
return -EOPNOTSUPP to indicate to resctrl that the counter assignment mode is not configurable.

> 
>> +			ret = -EINVAL;
>> +			rdt_last_cmd_puts("Counter assignment mode is not configurable\n");
>> +			goto out_unlock;
>> +		}
>> +
>>  		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>>  		if (ret)
>>  			goto out_unlock;
> 
 
Thanks,

Ben