Re: [PATCH 27/33] arm_mpam: Track bandwidth counter state for power management

Zeng Heng
2025-11-10T13:50:07Z

On 2025/11/7 20:34, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
>
> Bandwidth counters need to run continuously to correctly reflect the
> bandwidth.
>
> Save the counter state when the hardware is reset due to CPU hotplug.
> Add struct mbwu_state to track the bandwidth counter. Support for
> tracking overflow with the same structure will be added in a
> subsequent commit.
>
> Cc: Zeng Heng <zengheng4@huawei.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
> Changes since v3:
> Drop tags
> Fix correction accounting
> Split out overflow checking
> ---
> drivers/resctrl/mpam_devices.c | 126 +++++++++++++++++++++++++++++++-
> drivers/resctrl/mpam_internal.h | 21 +++++-
> 2 files changed, 145 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 86abbac5e1ad..2d1cef824b8e 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -994,6 +994,7 @@ static void __ris_msmon_read(void *arg)
> struct mon_read *m = arg;
> struct mon_cfg *ctx = m->ctx;
> struct mpam_msc_ris *ris = m->ris;
> + struct msmon_mbwu_state *mbwu_state;
> struct mpam_props *rprops = &ris->props;
> struct mpam_msc *msc = m->ris->vmsc->msc;
> u32 mon_sel, ctl_val, flt_val, cur_ctl, cur_flt;
> @@ -1024,11 +1025,21 @@ static void __ris_msmon_read(void *arg)
> now = mpam_read_monsel_reg(msc, CSU);
> if (mpam_has_feature(mpam_feat_msmon_csu_hw_nrdy, rprops))
> nrdy = now & MSMON___NRDY;
> + now = FIELD_GET(MSMON___VALUE, now);
> break;
> case mpam_feat_msmon_mbwu:
> now = mpam_read_monsel_reg(msc, MBWU);
> if (mpam_has_feature(mpam_feat_msmon_mbwu_hw_nrdy, rprops))
> nrdy = now & MSMON___NRDY;
> + now = FIELD_GET(MSMON___VALUE, now);
> +
> + if (nrdy)
> + break;
> +
> + mbwu_state = &ris->mbwu_state[ctx->mon];
> +
> + /* Include bandwidth consumed before the last hardware reset */
> + now += mbwu_state->correction;
> break;
> default:
> m->err = -EINVAL;
> @@ -1041,7 +1052,6 @@ static void __ris_msmon_read(void *arg)
> return;
> }
>
> - now = FIELD_GET(MSMON___VALUE, now);
> *m->val += now;
> }
>
> @@ -1239,6 +1249,67 @@ static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid,
> mutex_unlock(&msc->part_sel_lock);
> }
>
> +/* Call with msc cfg_lock held */
> +static int mpam_restore_mbwu_state(void *_ris)
> +{
> + int i;
> + struct mon_read mwbu_arg;
> + struct mpam_msc_ris *ris = _ris;
> +
> + for (i = 0; i < ris->props.num_mbwu_mon; i++) {
> + if (ris->mbwu_state[i].enabled) {
> + mwbu_arg.ris = ris;
> + mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
> + mwbu_arg.type = mpam_feat_msmon_mbwu;
> +
> + __ris_msmon_read(&mwbu_arg);
> + }
> + }
> +
> + return 0;
> +}
> +
> +/* Call with MSC cfg_lock held */
> +static int mpam_save_mbwu_state(void *arg)
> +{
> + int i;
> + u64 val;
> + struct mon_cfg *cfg;
> + u32 cur_flt, cur_ctl, mon_sel;
> + struct mpam_msc_ris *ris = arg;
> + struct msmon_mbwu_state *mbwu_state;
> + struct mpam_msc *msc = ris->vmsc->msc;
> +
> + for (i = 0; i < ris->props.num_mbwu_mon; i++) {
> + mbwu_state = &ris->mbwu_state[i];
> + cfg = &mbwu_state->cfg;
> +
> + if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
> + return -EIO;
> +
> + mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, i) |
> + FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
> + mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
> +
> + cur_flt = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
> + cur_ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
> +
> + val = mpam_read_monsel_reg(msc, MBWU);
> + mpam_write_monsel_reg(msc, MBWU, 0);
> +
> + cfg->mon = i;
> + cfg->pmg = FIELD_GET(MSMON_CFG_x_FLT_PMG, cur_flt);
> + cfg->match_pmg = FIELD_GET(MSMON_CFG_x_CTL_MATCH_PMG, cur_ctl);
> + cfg->partid = FIELD_GET(MSMON_CFG_x_FLT_PARTID, cur_flt);
> + mbwu_state->correction += val;
> + mbwu_state->enabled = FIELD_GET(MSMON_CFG_x_CTL_EN, cur_ctl);
> + mpam_mon_sel_unlock(msc);
> + }
> +
> + return 0;
> +}
> +
> static void mpam_init_reset_cfg(struct mpam_config *reset_cfg)
> {
> *reset_cfg = (struct mpam_config) {
> @@ -1310,6 +1381,9 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
> * for non-zero partid may be lost while the CPUs are offline.
> */
> ris->in_reset_state = online;
> +
> + if (mpam_is_enabled() && !online)
> + mpam_touch_msc(msc, &mpam_save_mbwu_state, ris);
> }
> mutex_unlock(&msc->cfg_lock);
> }
> @@ -1364,6 +1438,9 @@ static void mpam_reprogram_msc(struct mpam_msc *msc)
> mpam_touch_msc(msc, __write_config, &arg);
> }
> ris->in_reset_state = reset;
> +
> + if (mpam_has_feature(mpam_feat_msmon_mbwu, &ris->props))
> + mpam_touch_msc(msc, &mpam_restore_mbwu_state, ris);
> }
> mutex_unlock(&msc->cfg_lock);
> }
> @@ -2117,7 +2194,22 @@ static void mpam_unregister_irqs(void)
>
> static void __destroy_component_cfg(struct mpam_component *comp)
> {
> + struct mpam_msc *msc;
> + struct mpam_vmsc *vmsc;
> + struct mpam_msc_ris *ris;
> +
> + lockdep_assert_held(&mpam_list_lock);
> +
> add_to_garbage(comp->cfg);
> + list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
> + msc = vmsc->msc;
> +
> + if (mpam_mon_sel_lock(msc)) {
> + list_for_each_entry(ris, &vmsc->ris, vmsc_list)
> + add_to_garbage(ris->mbwu_state);
> + mpam_mon_sel_unlock(msc);
> + }
> + }
> }
>
> static void mpam_reset_component_cfg(struct mpam_component *comp)
> @@ -2141,6 +2233,8 @@ static void mpam_reset_component_cfg(struct mpam_component *comp)
>
> static int __allocate_component_cfg(struct mpam_component *comp)
> {
> + struct mpam_vmsc *vmsc;
> +
> mpam_assert_partid_sizes_fixed();
>
> if (comp->cfg)
> @@ -2158,6 +2252,36 @@ static int __allocate_component_cfg(struct mpam_component *comp)
>
> mpam_reset_component_cfg(comp);
>
> + list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
> + struct mpam_msc *msc;
> + struct mpam_msc_ris *ris;
> + struct msmon_mbwu_state *mbwu_state;
> +
> + if (!vmsc->props.num_mbwu_mon)
> + continue;
> +
> + msc = vmsc->msc;
> + list_for_each_entry(ris, &vmsc->ris, vmsc_list) {
> + if (!ris->props.num_mbwu_mon)
> + continue;
> +
> + mbwu_state = kcalloc(ris->props.num_mbwu_mon,
> + sizeof(*ris->mbwu_state),
> + GFP_KERNEL);
> + if (!mbwu_state) {
> + __destroy_component_cfg(comp);
> + return -ENOMEM;
> + }
> +
> + init_garbage(&mbwu_state[0].garbage);
> +
> + if (mpam_mon_sel_lock(msc)) {
> + ris->mbwu_state = mbwu_state;
> + mpam_mon_sel_unlock(msc);
> + }
> + }
> + }
> +
> return 0;
> }
>
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index d8f8e29987e0..1f2b04b7703e 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -91,7 +91,10 @@ struct mpam_msc {
> */
> struct mutex part_sel_lock;
>
> - /* cfg_lock protects the msc configuration. */
> + /*
> + * cfg_lock protects the msc configuration and guards against mbwu_state
> + * and save and restore racing.
> + */
> struct mutex cfg_lock;
>
> /*
> @@ -200,6 +203,19 @@ struct mon_cfg {
> enum mon_filter_options opts;
> };
>
> +/* Changes to msmon_mbwu_state are protected by the msc's mon_sel_lock. */
> +struct msmon_mbwu_state {
> + bool enabled;
> + struct mon_cfg cfg;
> +
> + /*
> + * The value to add to the new reading to account for power management.
> + */
> + u64 correction;
> +
> + struct mpam_garbage garbage;
> +};
> +
> struct mpam_class {
> /* mpam_components in this class */
> struct list_head components;
> @@ -293,6 +309,9 @@ struct mpam_msc_ris {
> /* parent: */
> struct mpam_vmsc *vmsc;
>
> + /* msmon mbwu configuration is preserved over reset */
> + struct msmon_mbwu_state *mbwu_state;
> +
> struct mpam_garbage garbage;
> };
>

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