Re: [PATCH 28/33] arm_mpam: Consider overflow in bandwidth counter state

Zeng Heng
2025-11-10T13:50:49Z

On 2025/11/7 20:34, Ben Horgan wrote:
> Use the overflow status bit to track overflow on each bandwidth counter
> read and add the counter size to the correction when overflow is detected.
>
> This assumes that only a single overflow has occurred since the last read
> of the counter. Overflow interrupts, on hardware that supports them could
> be used to remove this limitation.
>
> Cc: Zeng Heng <zengheng4@huawei.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
> drivers/resctrl/mpam_devices.c | 24 ++++++++++++++++++++++--
> drivers/resctrl/mpam_internal.h | 3 ++-
> 2 files changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 2d1cef824b8e..eea082dfcddc 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -986,11 +986,18 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
> }
> }
>
> +static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
> +{
> + /* TODO: scaling, and long counters */
> + return BIT_ULL(hweight_long(MSMON___VALUE));
> +}
> +
> static void __ris_msmon_read(void *arg)
> {
> u64 now;
> bool nrdy = false;
> bool config_mismatch;
> + bool overflow;
> struct mon_read *m = arg;
> struct mon_cfg *ctx = m->ctx;
> struct mpam_msc_ris *ris = m->ris;
> @@ -1012,13 +1019,20 @@ static void __ris_msmon_read(void *arg)
> * This saves waiting for 'nrdy' on subsequent reads.
> */
> read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> + overflow = cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS;
> +
> clean_msmon_ctl_val(&cur_ctl);
> gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
> config_mismatch = cur_flt != flt_val ||
> cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
>
> - if (config_mismatch)
> + if (config_mismatch) {
> write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> + overflow = false;
> + } else if (overflow) {
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
> + cur_ctl & ~MSMON_CFG_x_CTL_OFLOW_STATUS);
> + }
>
> switch (m->type) {
> case mpam_feat_msmon_csu:
> @@ -1038,7 +1052,13 @@ static void __ris_msmon_read(void *arg)
>
> mbwu_state = &ris->mbwu_state[ctx->mon];
>
> - /* Include bandwidth consumed before the last hardware reset */
> + if (overflow)
> + mbwu_state->correction += mpam_msmon_overflow_val(m->type);
> +
> + /*
> + * Include bandwidth consumed before the last hardware reset and
> + * a counter size increment for each overflow.
> + */
> now += mbwu_state->correction;
> break;
> default:
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 1f2b04b7703e..7c99d4f3dc9c 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -209,7 +209,8 @@ struct msmon_mbwu_state {
> struct mon_cfg cfg;
>
> /*
> - * The value to add to the new reading to account for power management.
> + * The value to add to the new reading to account for power management,
> + * and overflow.
> */
> u64 correction;
>

Reviewed-by: Zeng Heng <zengheng4@huawei.com>