Re: [PATCH v2 27/29] arm_mpam: Add helper to reset saved mbwu state

James Morse
2025-10-10T16:53:40Z

Hi Fenghua,

On 26/09/2025 05:11, Fenghua Yu wrote:
> On 9/10/25 13:43, James Morse wrote:
>> resctrl expects to reset the bandwidth counters when the filesystem
>> is mounted.
>>
>> To allow this, add a helper that clears the saved mbwu state. Instead
>> of cross calling to each CPU that can access the component MSC to
>> write to the counter, set a flag that causes it to be zero'd on the
>> the next read. This is easily done by forcing a configuration update.
>>
>> Signed-off-by: James Morse <james.morse@arm.com>
>
> Other than the following minor change,
>
> Reviewed-by: Fenghua Yu <fenghuay@nvdia.com>

Thanks!

>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index 3080a81f0845..8254d6190ca2 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c

>>   @@ -1245,6 +1257,37 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg
>> *ctx,
>>       return err;
>>   }
>>   +void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct mon_cfg *ctx)
>> +{
>> +    int idx;
>> +    struct mpam_msc *msc;
>> +    struct mpam_vmsc *vmsc;
>> +    struct mpam_msc_ris *ris;
>> +
>> +    if (!mpam_is_enabled())
>> +        return;
>> +
>> +    idx = srcu_read_lock(&mpam_srcu);

> guard(srcu)(&mpam_srcu);

Yeah, Jonathan had already suggested it.

>> +    list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
>> +        if (!mpam_has_feature(mpam_feat_msmon_mbwu, &vmsc->props))
>> +            continue;
>> +
>> +        msc = vmsc->msc;
>> +        list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
>> +            if (!mpam_has_feature(mpam_feat_msmon_mbwu, &ris->props))
>> +                continue;
>> +
>> +            if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
>> +                continue;
>> +
>> +            ris->mbwu_state[ctx->mon].correction = 0;
>> +            ris->mbwu_state[ctx->mon].reset_on_next_read = true;
>> +            mpam_mon_sel_unlock(msc);
>> +        }
>> +    }
>> +    srcu_read_unlock(&mpam_srcu, idx);
>> +}

Thanks,

James