Re: [PATCH RFC v2 08/17] RISC-V: QoS: add resctrl interface for CBQRI controllers

[Reinette Chatre]

Hi Drew,

On 2/18/26 1:49 PM, Drew Fustini wrote:
> On Fri, Feb 13, 2026 at 03:30:44PM -0800, Reinette Chatre wrote:
>> On 1/28/26 12:27 PM, Drew Fustini wrote:

>>> +void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
>>> +{
>>> +	*closid = ((u32)~0); /* refer to X86_RESCTRL_BAD_CLOSID */
>>
>> The name is actually X86_RESCTRL_EMPTY_CLOSID - and if RISC-V also needs it we could
>> make it generally available.A
> 
> There is no dependency between closid (RCID for CBQRI) and rmid (MCID
> for CBQRI), so resctrl_arch_rmid_idx_decode() is essentially the same
> for RISC-V.
> 
> What do you think would be the best way to share that between X86 and
> RISC-V?
> 
> Or is it is simpler to just defiend RISCV_RESCTRL_EMPTY_CLOSID?

Thinking about this more, yes, I do think this will be simplest since
a central define would force this on MPAM that does not seem appropriate.

...

> 
> CBQRI controllers are accessible by all harts (e.g. cpus) through mmio
> registers so access should not burden other harts. I think I will modify
> the implementation to just directly read/write the mmio registers when
> necessary rather than caching them in ctrl_val.

fyi ... resctrl is starting to show some signs of support for this. Please see
ab0308aee381 ("x86,fs/resctrl: Handle events that can be read from any CPU")
related to the monitoring code. Support for monitoring is not general yet
though since the default L3 events are still assumed to require reading from
CPU in the domain.

...

>>> +	err = qos_init_domain_ctrlval(res, domain);
>>> +	if (err)
>>> +		goto err_free_domain;
>>> +
>>> +	if (cbqri_res) {
>>> +		list_add_tail(&domain->hdr.list, &cbqri_res->resctrl_res.ctrl_domains);
>>
>> There is an expectation that the domain list be sorted. For reference, resctrl_find_domain().
> 
> Thank you for letting me know. I'll work on sorting the domains before
> adding to the list.

resctrl_find_domain() can help with this. If the domain is not found it returns
NULL and also returns the first domain with id bigger than the input id via a
parameter that can be used to insert a new domain in the right place.

Reinette