linux-stable/fs/bcachefs/time_stats.h
Darrick J. Wong be28368b2c bcachefs: time_stats: shrink time_stat_buffer for better alignment
Shrink this percpu object by one array element so that the object size
becomes exactly 512 bytes.  This will lead to more efficient memory use,
hopefully.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
2024-03-13 21:38:03 -04:00

159 lines
4.3 KiB
C

/* 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 */