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

Ben Horgan
2025-11-07T12:37:50Z

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;
};

--
2.43.0