Hi James,
On 9/9/25 17:56, James Morse wrote:
> Hi Ben,
>
> On 28/08/2025 14:12, Ben Horgan wrote:
>> On 8/22/25 16:29, James Morse wrote:
>>> CPUs can generate traffic with a range of PARTID and PMG values,
>>> but each MSC may have its own maximum size for these fields.
>>> Before MPAM can be used, the driver needs to probe each RIS on
>>> each MSC, to find the system-wide smallest value that can be used.
>>>
>>> While doing this, RIS entries that firmware didn't describe are create
>>> under MPAM_CLASS_UNKNOWN.
>>>
>>> While we're here, implement the mpam_register_requestor() call
>>> for the arch code to register the CPU limits. Future callers of this
>>> will tell us about the SMMU and ITS.
>
>>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>>> index 9d6516f98acf..012e09e80300 100644
>>> --- a/drivers/resctrl/mpam_devices.c
>>> +++ b/drivers/resctrl/mpam_devices.c
>>> @@ -106,6 +116,74 @@ static inline u32 _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg)
>
>>> +int mpam_register_requestor(u16 partid_max, u8 pmg_max)
>>> +{
>>> + int err = 0;
>>> +
>>> + lockdep_assert_irqs_enabled();
>>> +
>>> + spin_lock(&partid_max_lock);
>>> + if (!partid_max_init) {
>>> + mpam_partid_max = partid_max;
>>> + mpam_pmg_max = pmg_max;
>>> + partid_max_init = true;
>>> + } else if (!partid_max_published) {
>>> + mpam_partid_max = min(mpam_partid_max, partid_max);
>>> + mpam_pmg_max = min(mpam_pmg_max, pmg_max);
>
>> Do we really need to reduce these maximum here? If, say, we add an SMMU
>> requester which supports fewer partids than the cpus don't we want to be
>> able to carry on using those partids from the cpus. In this case the
>> SMMU requestor can, without risk of error interrupts, just use all the
>> partids it supports.
>
> How would it do that?
>
> We're probably going to expose that SMMU, or the devices behind it, via resctrl. You can
> create 10 control groups in resctrl - but can't assign the SMMU/devices to the last two
> because it doesn't actually support that many...
Ok. If that's how it's going to be exposed to the user then it make sense.
>
>
> Thanks,
>
> James
Thanks,
Ben
