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+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * bch2_time_stats - collect statistics on events that have a duration, with nicely
+ * formatted textual output on demand
+ *
+ * - percpu buffering of event collection: cheap enough to shotgun
+ * everywhere without worrying about overhead
+ *
+ * tracks:
+ * - number of events
+ * - maximum event duration ever seen
+ * - sum of all event durations
+ * - average event duration, standard and weighted
+ * - standard deviation of event durations, standard and weighted
+ * and analagous statistics for the frequency of events
+ *
+ * We provide both mean and weighted mean (exponentially weighted), and standard
+ * deviation and weighted standard deviation, to give an efficient-to-compute
+ * view of current behaviour versus. average behaviour - "did this event source
+ * just become wonky, or is this typical?".
+ *
+ * Particularly useful for tracking down latency issues.
+ */
+#ifndef _BCACHEFS_TIME_STATS_H
+#define _BCACHEFS_TIME_STATS_H
+
+#include <linux/sched/clock.h>
+#include <linux/spinlock_types.h>
+#include <linux/string.h>
+
+#include "mean_and_variance.h"
+
+struct time_unit {
+ const char *name;
+ u64 nsecs;
+};
+
+/*
+ * given a nanosecond value, pick the preferred time units for printing:
+ */
+const struct time_unit *bch2_pick_time_units(u64 ns);
+
+/*
+ * quantiles - do not use:
+ *
+ * Only enabled if bch2_time_stats->quantiles_enabled has been manually set - don't
+ * use in new code.
+ */
+
+#define NR_QUANTILES 15
+#define QUANTILE_IDX(i) inorder_to_eytzinger0(i, NR_QUANTILES)
+#define QUANTILE_FIRST eytzinger0_first(NR_QUANTILES)
+#define QUANTILE_LAST eytzinger0_last(NR_QUANTILES)
+
+struct quantiles {
+ struct quantile_entry {
+ u64 m;
+ u64 step;
+ } entries[NR_QUANTILES];
+};
+
+struct time_stat_buffer {
+ unsigned nr;
+ struct time_stat_buffer_entry {
+ u64 start;
+ u64 end;
+ } entries[31];
+};
+
+struct bch2_time_stats {
+ spinlock_t lock;
+ bool have_quantiles;
+ /* all fields are in nanoseconds */
+ u64 min_duration;
+ u64 max_duration;
+ u64 total_duration;
+ u64 max_freq;
+ u64 min_freq;
+ u64 last_event;
+ u64 last_event_start;
+
+ struct mean_and_variance duration_stats;
+ struct mean_and_variance freq_stats;
+
+/* default weight for weighted mean and variance calculations */
+#define TIME_STATS_MV_WEIGHT 8
+
+ struct mean_and_variance_weighted duration_stats_weighted;
+ struct mean_and_variance_weighted freq_stats_weighted;
+ struct time_stat_buffer __percpu *buffer;
+};
+
+struct bch2_time_stats_quantiles {
+ struct bch2_time_stats stats;
+ struct quantiles quantiles;
+};
+
+static inline struct quantiles *time_stats_to_quantiles(struct bch2_time_stats *stats)
+{
+ return stats->have_quantiles
+ ? &container_of(stats, struct bch2_time_stats_quantiles, stats)->quantiles
+ : NULL;
+}
+
+void __bch2_time_stats_clear_buffer(struct bch2_time_stats *, struct time_stat_buffer *);
+void __bch2_time_stats_update(struct bch2_time_stats *stats, u64, u64);
+
+/**
+ * time_stats_update - collect a new event being tracked
+ *
+ * @stats - bch2_time_stats to update
+ * @start - start time of event, recorded with local_clock()
+ *
+ * The end duration of the event will be the current time
+ */
+static inline void bch2_time_stats_update(struct bch2_time_stats *stats, u64 start)
+{
+ __bch2_time_stats_update(stats, start, local_clock());
+}
+
+/**
+ * track_event_change - track state change events
+ *
+ * @stats - bch2_time_stats to update
+ * @v - new state, true or false
+ *
+ * Use this when tracking time stats for state changes, i.e. resource X becoming
+ * blocked/unblocked.
+ */
+static inline bool track_event_change(struct bch2_time_stats *stats, bool v)
+{
+ if (v != !!stats->last_event_start) {
+ if (!v) {
+ bch2_time_stats_update(stats, stats->last_event_start);
+ stats->last_event_start = 0;
+ } else {
+ stats->last_event_start = local_clock() ?: 1;
+ return true;
+ }
+ }
+
+ return false;
+}
+
+void bch2_time_stats_exit(struct bch2_time_stats *);
+void bch2_time_stats_init(struct bch2_time_stats *);
+
+static inline void bch2_time_stats_quantiles_exit(struct bch2_time_stats_quantiles *statq)
+{
+ bch2_time_stats_exit(&statq->stats);
+}
+static inline void bch2_time_stats_quantiles_init(struct bch2_time_stats_quantiles *statq)
+{
+ bch2_time_stats_init(&statq->stats);
+ statq->stats.have_quantiles = true;
+ memset(&statq->quantiles, 0, sizeof(statq->quantiles));
+}
+
+#endif /* _BCACHEFS_TIME_STATS_H */