Re: [RFC v2] arm,x86,fs/resctrl: Generic schema description Proof of Concept

Hi Reinette,

Thanks for the patches. I am yet to look at all the patches.

On 8/6/2026 12:11 PM, Reinette Chatre wrote:
> Hi Tony,
> 
> On 8/6/26 10:04 AM, Luck, Tony wrote:
>> On Wed, Aug 05, 2026 at 04:57:04PM -0700, Reinette Chatre wrote:
>>> Hi Ben,
>>>
>>> On 8/5/26 9:59 AM, Ben Horgan wrote:
>>>> Just given a go at running this on a model with MPAM and I can mount resctrl with this
>>>> small patch to initialise the emulated_by lists so that list_empty() behaves.
>>>>
>>>> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
>>>> index 21dcbf5764cc..638095649151 100644
>>>> --- a/drivers/resctrl/mpam_resctrl.c
>>>> +++ b/drivers/resctrl/mpam_resctrl.c
>>>> @@ -1018,6 +1018,7 @@ static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
>>>>          case RDT_RESOURCE_L3:
>>>>                  mpam_ctrl->r_ctrl.type = RESCTRL_CTRL_BITMAP;
>>>>                  mpam_ctrl->r_ctrl.name = RESCTRL_CTRL_NAME_DEF;
>>>> +               INIT_LIST_HEAD(&mpam_ctrl->r_ctrl.emulated_by);
>>>>                  INIT_LIST_HEAD_RCU(&mpam_ctrl->r_ctrl.domains);
>>>>                  __set_bit(RESCTRL_BITMAP_FLAG_SPARSE, mpam_ctrl->r_ctrl.bitmap.flags);
>>>>                  mpam_ctrl->r_ctrl.bitmap.cbm_len = class->props.cpbm_wd;
>>>> @@ -1048,6 +1049,7 @@ static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
>>>>                  r->ctrl_scope = RESCTRL_L3_CACHE;
>>>>                  mpam_ctrl->r_ctrl.type = RESCTRL_CTRL_SCALAR;
>>>>                  mpam_ctrl->r_ctrl.name = RESCTRL_CTRL_NAME_DEF;
>>>> +               INIT_LIST_HEAD(&mpam_ctrl->r_ctrl.emulated_by);
>>>>                  INIT_LIST_HEAD_RCU(&mpam_ctrl->r_ctrl.domains);
>>>>
>>>>                  r->bw_throttle_mode = THREAD_THROTTLE_UNDEFINED;
>>>
>>> Thank you for this. Added this and it is now available in branch resctrl/controls_rfc_v2.1
>>
>> Is same needed for x86? I don't see any initialization of the
>> "r_ctrl.emulated_by" lists in similar initialization functions.
> x86 "emulated_by" list initialization should be in both branches.
> 
> Branch resctrl/controls_rfc_v2.1 combined all "emulated_by" list initialization
> (for x86 and MPAM) into commit:
> 3407e523c988 ("fs/resctrl: Introduce emulated controls and control mode")
> 
> In the original resctrl/controls_rfc_v2 the x86 "emulated_by" list initialization can
> be found in commit fbed64f80515 ("x86/resctrl: SAMPLE: Emulated controls")
> 

Looking at the commit:

commit 3407e523c988 ("fs/resctrl: Introduce emulated controls and 
control mode")

Based on the patch description, emulated controls are intended to be 
used only when there is a difference between the native and legacy 
controls. If no such difference exists, both modes should operate 
identically.

For MBA(AMD) and GMBA, there does not appear to be any difference 
between the two modes. Is that understanding correct?

Thanks
Babu