Re: [PATCH 26/33] arm_mpam: Add mpam_msmon_read() to read monitor value

Gavin Shan
2025-11-09T23:13:24Z

Hi Ben,

On 11/7/25 10:34 PM, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
>
> Reading a monitor involves configuring what you want to monitor, and
> reading the value. Components made up of multiple MSC may need values
> from each MSC. MSCs may take time to configure, returning 'not ready'.
> The maximum 'not ready' time should have been provided by firmware.
>
> Add mpam_msmon_read() to hide all this. If (one of) the MSC returns
> not ready, then wait the full timeout value before trying again.
>
> CC: Shanker Donthineni <sdonthineni@nvidia.com>
> Cc: Shaopeng Tan (Fujitsu) <tan.shaopeng@fujitsu.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Tested-by: Peter Newman <peternewman@google.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
> Changes since v3:
> Add tag - thanks
> Bring config_mismatch into this commit (Jonathan)
> whitespace
> ---
> drivers/resctrl/mpam_devices.c | 237 ++++++++++++++++++++++++++++++++
> drivers/resctrl/mpam_internal.h | 19 +++
> 2 files changed, 256 insertions(+)
>

With below minor comments addressed:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index f51ffb1400db..86abbac5e1ad 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -886,6 +886,243 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
> return 0;
> }
>
> +struct mon_read {
> + struct mpam_msc_ris *ris;
> + struct mon_cfg *ctx;
> + enum mpam_device_features type;
> + u64 *val;
> + int err;
> +};
> +
> +static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> + u32 *flt_val)
> +{
> + struct mon_cfg *ctx = m->ctx;
> +
> + /*
> + * For CSU counters its implementation-defined what happens when not
> + * filtering by partid.
> + */
> + *ctl_val = MSMON_CFG_x_CTL_MATCH_PARTID;
> +
> + *flt_val = FIELD_PREP(MSMON_CFG_x_FLT_PARTID, ctx->partid);
> +
> + if (m->ctx->match_pmg) {
> + *ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
> + *flt_val |= FIELD_PREP(MSMON_CFG_x_FLT_PMG, ctx->pmg);
> + }
> +
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + *ctl_val |= MSMON_CFG_CSU_CTL_TYPE_CSU;
> +
> + if (mpam_has_feature(mpam_feat_msmon_csu_xcl, &m->ris->props))
> + *flt_val |= FIELD_PREP(MSMON_CFG_CSU_FLT_XCL,
> + ctx->csu_exclude_clean);

{} missed here.

> +
> + break;
> + case mpam_feat_msmon_mbwu:
> + *ctl_val |= MSMON_CFG_MBWU_CTL_TYPE_MBWU;
> +
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_rwbw, &m->ris->props))
> + *flt_val |= FIELD_PREP(MSMON_CFG_MBWU_FLT_RWBW, ctx->opts);
> +
> + break;
> + default:
> + return;

s/return/break

We may add a error message here:

pr_warn("Unsupported feature %d\n", m->type);

> + }
> +}
> +
> +static void read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> + u32 *flt_val)
> +{
> + struct mpam_msc *msc = m->ris->vmsc->msc;
> +
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + *ctl_val = mpam_read_monsel_reg(msc, CFG_CSU_CTL);
> + *flt_val = mpam_read_monsel_reg(msc, CFG_CSU_FLT);
> + return;
> + case mpam_feat_msmon_mbwu:
> + *ctl_val = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
> + *flt_val = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
> + return;
> + default:
> + return;
> + }
> +}

s/return/break for all cases, and maybe a warning message for the
default case.

> +
> +/* Remove values set by the hardware to prevent apparent mismatches. */
> +static void clean_msmon_ctl_val(u32 *cur_ctl)
> +{
> + *cur_ctl &= ~MSMON_CFG_x_CTL_OFLOW_STATUS;
> +}
> +

May be worthy be to a inline function.

> +static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
> + u32 flt_val)
> +{
> + struct mpam_msc *msc = m->ris->vmsc->msc;
> +
> + /*
> + * Write the ctl_val with the enable bit cleared, reset the counter,
> + * then enable counter.
> + */
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + mpam_write_monsel_reg(msc, CFG_CSU_FLT, flt_val);
> + mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
> + mpam_write_monsel_reg(msc, CSU, 0);
> + mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
> + break;
> + case mpam_feat_msmon_mbwu:
> + mpam_write_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
> + /* Counting monitors require NRDY to be reset by software */
> + mpam_write_monsel_reg(msc, MBWU, 0);
> + break;
> + default:
> + return;

s/return/break, and maybe a warning message for the default case.

> + }
> +}
> +
> +static void __ris_msmon_read(void *arg)
> +{
> + u64 now;
> + bool nrdy = false;
> + bool config_mismatch;
> + struct mon_read *m = arg;
> + struct mon_cfg *ctx = m->ctx;
> + struct mpam_msc_ris *ris = m->ris;
> + 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;
> +
> + if (!mpam_mon_sel_lock(msc)) {
> + m->err = -EIO;
> + return;
> + }
> + mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
> + FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
> + mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
> +
> + /*
> + * Read the existing configuration to avoid re-writing the same values.
> + * This saves waiting for 'nrdy' on subsequent reads.
> + */
> + read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> + 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)
> + write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> +
> + switch (m->type) {
> + case mpam_feat_msmon_csu:
> + now = mpam_read_monsel_reg(msc, CSU);
> + if (mpam_has_feature(mpam_feat_msmon_csu_hw_nrdy, rprops))
> + nrdy = now & MSMON___NRDY;
> + 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;
> + break;
> + default:
> + m->err = -EINVAL;
> + break;

This 'break' can be droped.

> + }
> + mpam_mon_sel_unlock(msc);
> +
> + if (nrdy) {
> + m->err = -EBUSY;
> + return;
> + }
> +
> + now = FIELD_GET(MSMON___VALUE, now);
> + *m->val += now;
> +}
> +
> +static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)
> +{
> + int err, any_err = 0;
> + struct mpam_vmsc *vmsc;
> +
> + guard(srcu)(&mpam_srcu);
> + list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
> + srcu_read_lock_held(&mpam_srcu)) {
> + struct mpam_msc *msc = vmsc->msc;
> + struct mpam_msc_ris *ris;
> +
> + list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
> + srcu_read_lock_held(&mpam_srcu)) {
> + arg->ris = ris;
> +
> + err = smp_call_function_any(&msc->accessibility,
> + __ris_msmon_read, arg,
> + true);
> + if (!err && arg->err)
> + err = arg->err;
> +
> + /*
> + * Save one error to be returned to the caller, but
> + * keep reading counters so that get reprogrammed. On
> + * platforms with NRDY this lets us wait once.
> + */
> + if (err)
> + any_err = err;
> + }
> + }
> +
> + return any_err;
> +}
> +
> +int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
> + enum mpam_device_features type, u64 *val)
> +{
> + int err;
> + struct mon_read arg;
> + u64 wait_jiffies = 0;
> + struct mpam_props *cprops = &comp->class->props;
> +
> + might_sleep();
> +
> + if (!mpam_is_enabled())
> + return -EIO;
> +
> + if (!mpam_has_feature(type, cprops))
> + return -EOPNOTSUPP;
> +
> + arg = (struct mon_read) {
> + .ctx = ctx,
> + .type = type,
> + .val = val,
> + };
> + *val = 0;
> +
> + err = _msmon_read(comp, &arg);
> + if (err == -EBUSY && comp->class->nrdy_usec)
> + wait_jiffies = usecs_to_jiffies(comp->class->nrdy_usec);
> +
> + while (wait_jiffies)
> + wait_jiffies = schedule_timeout_uninterruptible(wait_jiffies);
> +
> + if (err == -EBUSY) {
> + arg = (struct mon_read) {
> + .ctx = ctx,
> + .type = type,
> + .val = val,
> + };
> + *val = 0;
> +
> + err = _msmon_read(comp, &arg);
> + }
> +
> + return err;
> +}
> +
> static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
> {
> u32 num_words, msb;
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index e59c0f4d9ada..d8f8e29987e0 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -184,6 +184,22 @@ struct mpam_props {
> #define mpam_set_feature(_feat, x) set_bit(_feat, (x)->features)
> #define mpam_clear_feature(_feat, x) clear_bit(_feat, (x)->features)
>
> +/* The values for MSMON_CFG_MBWU_FLT.RWBW */
> +enum mon_filter_options {
> + COUNT_BOTH = 0,
> + COUNT_WRITE = 1,
> + COUNT_READ = 2,
> +};
> +
> +struct mon_cfg {
> + u16 mon;
> + u8 pmg;
> + bool match_pmg;
> + bool csu_exclude_clean;
> + u32 partid;
> + enum mon_filter_options opts;
> +};
> +
> struct mpam_class {
> /* mpam_components in this class */
> struct list_head components;
> @@ -327,6 +343,9 @@ void mpam_disable(struct work_struct *work);
> int mpam_apply_config(struct mpam_component *comp, u16 partid,
> struct mpam_config *cfg);
>
> +int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
> + enum mpam_device_features, u64 *val);
> +
> int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
> cpumask_t *affinity);
>
Thanks,
Gavin