Re: [PATCH v2 1/3] rv: add per-edge dwell-time statistics primitive
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From: Gabriele Monaco <gmonaco@redhat.com>
Date: 2026-09-24 07:21:20
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On Fri, 2026-09-11 at 14:34 +0200, Tobias Schaffner wrote:
quoted hunk ↗ jump to hunk
Add a small primitive that records, per automaton edge, how long the monitor dwelled before taking it with a count, a sum and a maximum. The counters are per-CPU and lock-free, so a monitor's hot path can update them without disabling interrupts and without perturbing the latency being measured. Keep the state and its entry timestamp in one word so nested transitions cannot charge a dwell to the wrong edge. Signed-off-by: Tobias Schaffner <tobias.schaffner@siemens.com> --- include/rv/edge_stat.h | 69 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 69 insertions(+) create mode 100644 include/rv/edge_stat.hdiff --git a/include/rv/edge_stat.h b/include/rv/edge_stat.h
...
+#define RV_STATE_BITS 8 +#define RV_STATE_MASK GENMASK(RV_STATE_BITS - 1, 0) +#define RV_TS_MASK GENMASK(BITS_PER_LONG - RV_STATE_BITS - 1, 0) + +#define da_state_of(w) ((unsigned int)((w) & RV_STATE_MASK)) +#define da_ts_of(w) ((u64)(w) >> RV_STATE_BITS) +#define da_state_pack(s, ts) (((((da_state_t)(ts)) & RV_TS_MASK) << RV_STATE_BITS) | \ + ((da_state_t)(s) & RV_STATE_MASK))
These are barely readable and error prone, can you use FIELD_GET()/FIELD_PREP()? Thanks, Gabriele
+
+static __always_inline
+void rv_edge_stat_account(struct rv_edge_stat *s, u64 dwell_ns)
+{
+ s64 max;
+ int i;
+
+ local64_inc(&s->count);
+ local64_add(dwell_ns, &s->sum_ns);
+
+ /* Keep the largest dwell; bound retries if a nested update races us.
*/
+ max = local64_read(&s->max_ns);
+ for (i = 0; dwell_ns > (u64)max; i++) {
+ if (i == MAX_DA_RETRY_RACING_EVENTS) {
+ WARN_ONCE(1, "rv: edge-stat max update exceeded %d
retries\n",
+ MAX_DA_RETRY_RACING_EVENTS);
+ break;
+ }
+ if (local64_try_cmpxchg(&s->max_ns, &max, dwell_ns))
+ break;
+ }
+}
+
+#endif /* CONFIG_RV_EDGE_STAT */
+
+#endif /* _RV_EDGE_STAT_H */