Re: [PATCH v2 1/2] perf/arm-cmn: Decouple wp_config registers from filter group number

Robin Murphy
2024-03-08T14:35:27Z

On 2024-03-07 11:09 pm, Ilkka Koskinen wrote:
> Previously, wp_config0/2 registers were used for primary match group and
> wp_config1/3 registers for secondary match group. In order to support
> tertiary match group, this patch decouples the registers and the groups.
>
> Signed-off-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
> ---
> drivers/perf/arm-cmn.c | 125 ++++++++++++++++++++++++++++++++++-------
> 1 file changed, 105 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 7e3aa7e2345f..29d46e0cf1cd 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -589,6 +589,13 @@ struct arm_cmn_hw_event {
> s8 dtc_idx[CMN_MAX_DTCS];
> u8 num_dns;
> u8 dtm_offset;
> +
> + /*
> + * WP config registers are divided to UP and DOWN events. We need to
> + * keep to track only one of them.
> + */
> + DECLARE_BITMAP(wp_cfg, 2 * CMN_MAX_XPS);

What I had in mind was a wp_idx field which works the same way as
dtm_idx, i.e. we just store the allocated index per relevant DN, since a
single event can never use *both* watchpoints on a single XP. Each index
then need only be 0 or 1 since they're already scoped by the watchpoint
direction of the base event, thus we should only need one bit per XP.

> +
> bool wide_sel;
> enum cmn_filter_select filter_sel;
> };
> @@ -1335,9 +1342,51 @@ static const struct attribute_group *arm_cmn_attr_groups[] = {
> NULL
> };
>
> -static int arm_cmn_wp_idx(struct perf_event *event)
> +static inline unsigned int arm_cmn_get_xp_idx(struct arm_cmn *cmn,
> + struct arm_cmn_node *xp)
> {
> - return CMN_EVENT_EVENTID(event) + CMN_EVENT_WP_GRP(event);
> + return ((unsigned long) xp - (unsigned long) cmn->xps) / sizeof(struct arm_cmn_node);
> +}
> +
> +static int arm_cmn_find_free_wp_idx(struct arm_cmn *cmn, struct arm_cmn_dtm *dtm,
> + struct perf_event *event)
> +{
> + int wp_idx = CMN_EVENT_EVENTID(event);
> +
> + if (dtm->wp_event[wp_idx] >= 0)
> + if (dtm->wp_event[++wp_idx] >= 0)
> + return -ENOSPC;
> +
> + return wp_idx;
> +}
> +
> +static int arm_cmn_get_assigned_wp_idx(struct arm_cmn *cmn,
> + struct arm_cmn_node *xp,
> + struct perf_event *event,
> + struct arm_cmn_hw_event *hw)
> +{
> + int xp_idx = arm_cmn_get_xp_idx(cmn, xp);
> +
> + if (test_bit(2 * xp_idx, hw->wp_cfg))
> + return CMN_EVENT_EVENTID(event);
> + else if (test_bit(2 * xp_idx + 1, hw->wp_cfg))
> + return CMN_EVENT_EVENTID(event) + 1;
> +
> + dev_err(cmn->dev, "Could't find the assigned wp_cfg\n");
> + return -EINVAL;
> +}

...and so for this we would only need more of a mild tweak to the
existing design, something like:

static int arm_cmn_get_wp_idx(struct perf_event *event, int pos)
{
struct arm_cmn_hw_event *hw = to_cmn_hw(event);

return CMN_EVENT_EVENTID(event) + test_bit(&hw->wp_idx, pos);
}

> +
> +static void arm_cmn_claim_wp_idx(struct arm_cmn *cmn,
> + struct arm_cmn_dtm *dtm,
> + struct perf_event *event,
> + struct arm_cmn_node *xp,
> + int wp_idx, unsigned int dtc)
> +{
> + struct arm_cmn_hw_event *hw = to_cmn_hw(event);
> + int xp_idx = arm_cmn_get_xp_idx(cmn, xp);
> +
> + dtm->wp_event[wp_idx] = hw->dtc_idx[dtc];
> + set_bit(2 * xp_idx + (wp_idx & 1), hw->wp_cfg);

This is recalculating way more than it needs to. It's only ever used
within for_each_hw_dn(), which already has all the information to hand
already - again, look at how hw->dtm_idx is managed. Furthermore I'd
also prefer to similarly not conflate management of the per-event state
with that of the DTM state (i.e. just have an arm_cmn_set_wp_idx() for
updating the event data).

> }
>
> static u32 arm_cmn_wp_config(struct perf_event *event)
> @@ -1519,12 +1568,16 @@ static void arm_cmn_event_start(struct perf_event *event, int flags)
> writeq_relaxed(CMN_CC_INIT, cmn->dtc[i].base + CMN_DT_PMCCNTR);
> cmn->dtc[i].cc_active = true;
> } else if (type == CMN_TYPE_WP) {
> - int wp_idx = arm_cmn_wp_idx(event);
> u64 val = CMN_EVENT_WP_VAL(event);
> u64 mask = CMN_EVENT_WP_MASK(event);
>
> for_each_hw_dn(hw, dn, i) {
> void __iomem *base = dn->pmu_base + CMN_DTM_OFFSET(hw->dtm_offset);
> + int wp_idx;
> +
> + wp_idx = arm_cmn_get_assigned_wp_idx(cmn, dn, event, hw);
> + if (wp_idx < 0)
> + return;
>
> writeq_relaxed(val, base + CMN_DTM_WPn_VAL(wp_idx));
> writeq_relaxed(mask, base + CMN_DTM_WPn_MASK(wp_idx));
> @@ -1549,10 +1602,13 @@ static void arm_cmn_event_stop(struct perf_event *event, int flags)
> i = hw->dtc_idx[0];
> cmn->dtc[i].cc_active = false;
> } else if (type == CMN_TYPE_WP) {
> - int wp_idx = arm_cmn_wp_idx(event);
> -
> for_each_hw_dn(hw, dn, i) {
> void __iomem *base = dn->pmu_base + CMN_DTM_OFFSET(hw->dtm_offset);
> + int wp_idx;
> +
> + wp_idx = arm_cmn_get_assigned_wp_idx(cmn, dn, event, hw);
> + if (wp_idx < 0)
> + continue;
>
> writeq_relaxed(0, base + CMN_DTM_WPn_MASK(wp_idx));
> writeq_relaxed(~0ULL, base + CMN_DTM_WPn_VAL(wp_idx));
> @@ -1574,8 +1630,20 @@ struct arm_cmn_val {
> bool cycles;
> };
>
> -static void arm_cmn_val_add_event(struct arm_cmn *cmn, struct arm_cmn_val *val,
> - struct perf_event *event)
> +static int arm_cmn_val_find_free_wp_config(struct perf_event *event,
> + struct arm_cmn_val *val, int dtm)
> +{
> + int wp_idx = CMN_EVENT_EVENTID(event);
> +
> + if (val->wp[dtm][wp_idx])
> + if (val->wp[dtm][++wp_idx])
> + return -ENOSPC;
> +
> + return wp_idx;
> +}
> +
> +static int arm_cmn_val_add_event(struct arm_cmn *cmn, struct arm_cmn_val *val,
> + struct perf_event *event)

This must never fail - the purpose of val_add_event is to fill in the
val structure with the combination of leader and sibling events which
have *already* passed their own event_init calls been declared valid as
a group. The body of validate_group then does the "what if?" version to
test whether the group would remain valid if the *current* event were to
be added.

The trick with the offset combine value relies on direct indexing to
work, so I think we need to rejig the structure slightly to track
distinct wp_count and wp_combine values (per direction) - that then
becomes nicely consistent with the relationship between dtm_count and
occupid, too.

> {
> struct arm_cmn_hw_event *hw = to_cmn_hw(event);
> struct arm_cmn_node *dn;
> @@ -1583,12 +1651,12 @@ static void arm_cmn_val_add_event(struct arm_cmn *cmn, struct arm_cmn_val *val,
> int i;
>
> if (is_software_event(event))
> - return;
> + return 0;
>
> type = CMN_EVENT_TYPE(event);
> if (type == CMN_TYPE_DTC) {
> val->cycles = true;
> - return;
> + return 0;
> }
>
> for_each_hw_dtc_idx(hw, dtc, idx)
> @@ -1605,9 +1673,14 @@ static void arm_cmn_val_add_event(struct arm_cmn *cmn, struct arm_cmn_val *val,
> if (type != CMN_TYPE_WP)
> continue;
>
> - wp_idx = arm_cmn_wp_idx(event);
> + wp_idx = arm_cmn_val_find_free_wp_config(event, val, dtm);
> + if (wp_idx < 0)
> + return -ENOSPC;
> +
> val->wp[dtm][wp_idx] = CMN_EVENT_WP_COMBINE(event) + 1;
> }
> +
> + return 0;
> }
>
> static int arm_cmn_validate_group(struct arm_cmn *cmn, struct perf_event *event)
> @@ -1629,9 +1702,15 @@ static int arm_cmn_validate_group(struct arm_cmn *cmn, struct perf_event *event)
> if (!val)
> return -ENOMEM;
>
> - arm_cmn_val_add_event(cmn, val, leader);
> - for_each_sibling_event(sibling, leader)
> - arm_cmn_val_add_event(cmn, val, sibling);
> + ret = arm_cmn_val_add_event(cmn, val, leader);
> + if (ret)
> + goto done;
> +
> + for_each_sibling_event(sibling, leader) {
> + ret = arm_cmn_val_add_event(cmn, val, sibling);
> + if (ret)
> + goto done;
> + }
>
> type = CMN_EVENT_TYPE(event);
> if (type == CMN_TYPE_DTC) {
> @@ -1656,8 +1735,8 @@ static int arm_cmn_validate_group(struct arm_cmn *cmn, struct perf_event *event)
> if (type != CMN_TYPE_WP)
> continue;
>
> - wp_idx = arm_cmn_wp_idx(event);
> - if (val->wp[dtm][wp_idx])
> + wp_idx = arm_cmn_val_find_free_wp_config(event, val, dtm);
> + if (wp_idx < 0)
> goto done;
>
> wp_cmb = val->wp[dtm][wp_idx ^ 1];
> @@ -1772,8 +1851,11 @@ static void arm_cmn_event_clear(struct arm_cmn *cmn, struct perf_event *event,
> struct arm_cmn_dtm *dtm = &cmn->dtms[hw->dn[i].dtm] + hw->dtm_offset;
> unsigned int dtm_idx = arm_cmn_get_index(hw->dtm_idx, i);
>
> - if (type == CMN_TYPE_WP)
> - dtm->wp_event[arm_cmn_wp_idx(event)] = -1;
> + if (type == CMN_TYPE_WP) {
> + int wp_idx = arm_cmn_get_assigned_wp_idx(cmn, &hw->dn[i], event, hw);
> +
> + dtm->wp_event[wp_idx] = -1;
> + }
>
> if (hw->filter_sel > SEL_NONE)
> hw->dn[i].occupid[hw->filter_sel].count--;
> @@ -1782,6 +1864,7 @@ static void arm_cmn_event_clear(struct arm_cmn *cmn, struct perf_event *event,
> writel_relaxed(dtm->pmu_config_low, dtm->base + CMN_DTM_PMU_CONFIG);
> }
> memset(hw->dtm_idx, 0, sizeof(hw->dtm_idx));
> + bitmap_zero(hw->wp_cfg, 2 * CMN_MAX_XPS);

Nit: I'd rather do this in terms of sizeof() so it's harder to break in
future. And since it's going to end up being a memset() anyway I'd then
probably just open-code that rather than mucking about with
bytes-to-bits calculations.

> for_each_hw_dtc_idx(hw, j, idx)
> cmn->dtc[j].counters[idx] = NULL;
> @@ -1835,10 +1918,11 @@ static int arm_cmn_event_add(struct perf_event *event, int flags)
> if (type == CMN_TYPE_XP) {
> input_sel = CMN__PMEVCNT0_INPUT_SEL_XP + dtm_idx;
> } else if (type == CMN_TYPE_WP) {
> - int tmp, wp_idx = arm_cmn_wp_idx(event);
> + int tmp, wp_idx;
> u32 cfg = arm_cmn_wp_config(event);
>
> - if (dtm->wp_event[wp_idx] >= 0)
> + wp_idx = arm_cmn_find_free_wp_idx(cmn, dtm, event);
> + if (wp_idx < 0)

TBH I'm not convinced it's even worth factoring out the "allocator"
here, since inline it can be as simple as:

int tmp, wp_idx = CMN_EVENT_EVENTID(event);
...
if (dtm->wp_event[wp_idx] && dtm->wp_event[++wp_idx])

(or perhaps follow the same while/if shape as for dtm_idx further up, if
you think it's worth being more clear than concise)

Thanks,
Robin.

> goto free_dtms;
>
> tmp = dtm->wp_event[wp_idx ^ 1];
> @@ -1847,7 +1931,8 @@ static int arm_cmn_event_add(struct perf_event *event, int flags)
> goto free_dtms;
>
> input_sel = CMN__PMEVCNT0_INPUT_SEL_WP + wp_idx;
> - dtm->wp_event[wp_idx] = hw->dtc_idx[d];
> +
> + arm_cmn_claim_wp_idx(cmn, dtm, event, dn, wp_idx, d);
> writel_relaxed(cfg, dtm->base + CMN_DTM_WPn_CONFIG(wp_idx));
> } else {
> struct arm_cmn_nodeid nid = arm_cmn_nid(cmn, dn->id);