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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 */
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