Re: [PATCH v2 23/29] arm_mpam: Add mpam_msmon_read() to read monitor value

Fenghua Yu
2025-09-25T02:30:40Z

Hi, James,

On 9/10/25 13:43, James Morse wrote:
> 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>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v1:
> * Added XCL support.
> * Merged FLT/CTL constants.
> * a spelling mistake in a comment.
> * moved structrues around.
> ---
> drivers/resctrl/mpam_devices.c | 226 ++++++++++++++++++++++++++++++++
> drivers/resctrl/mpam_internal.h | 19 +++
> 2 files changed, 245 insertions(+)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index cf190f896de1..1543c33c5d6a 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -898,6 +898,232 @@ 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);
> +
> + 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;
> + }
> +}
> +
> +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);
> + break;
> + 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);
> + break;
> + default:
> + return;
> + }
> +}
> +
> +/* 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;
> +}
> +
> +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, MBWU, 0);
> + mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
> + break;
> + default:
> + return;
> + }
> +}
> +
> +/* Call with MSC lock held */
> +static void __ris_msmon_read(void *arg)
> +{
> + u64 now;
> + bool nrdy = false;
> + 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);
> + if (cur_flt != flt_val || cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN))
> + 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;
> + }
> + 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, idx;
Can err be initialized to some error code e.g. -ENODEV?
> + struct mpam_msc *msc;
> + struct mpam_vmsc *vmsc;
> + struct mpam_msc_ris *ris;
> +
> + idx = srcu_read_lock(&mpam_srcu);
> + list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
> + msc = vmsc->msc;
> +
> + list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
> + arg->ris = ris;
> +
> + err = smp_call_function_any(&msc->accessibility,
> + __ris_msmon_read, arg,
> + true);
> + if (!err && arg->err)
> + err = arg->err;
> + if (err)
> + break;
> + }
> + if (err)
> + break;
> + }

comp->vmsc or vmsc->ris usually are not empty. But in some condition,
they can be empty. In that case, uninitialized err value may cause
unexpected behavior for the callers.

So it's better to initialize err to avoid any complexity.

> + srcu_read_unlock(&mpam_srcu, idx);
> +
> + return 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;
> +
> + memset(&arg, 0, sizeof(arg));
> + arg.ctx = ctx;
> + arg.type = type;
> + arg.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) {
> + memset(&arg, 0, sizeof(arg));
> + arg.ctx = ctx;
> + arg.type = type;
> + arg.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 81c4c2bfea3d..bb01e7dbde40 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -196,6 +196,22 @@ static inline void mpam_clear_feature(enum mpam_device_features feat,
> *supported &= ~(1 << feat);
> }
>
> +/* 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;
> @@ -343,6 +359,9 @@ 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.

-Fenghua