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timekeeping: Add percpu counter for tracking floor swap events

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The mgtime_floor value is a global variable for tracking the latest
fine-grained timestamp handed out. Because it's a global, track the
number of times that a new floor value is assigned.

Add a new percpu counter to the timekeeping code to track the number of
floor swap events that have occurred. A later patch will add a debugfs
file to display this counter alongside other stats involving multigrain
timestamps.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # documentation bits
Link: https://lore.kernel.org/all/20241002-mgtime-v10-2-d1c4717f5284@kernel.org
This commit is contained in:
Jeff Layton 2024-10-02 17:27:17 -04:00 committed by Thomas Gleixner
parent 70c8fd00a9
commit 96f9a366ec
4 changed files with 30 additions and 0 deletions
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1
include/linux/timekeeping.h
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@ -48,6 +48,7 @@ extern void ktime_get_coarse_real_ts64(struct timespec64 *ts);
/* Multigrain timestamp interfaces */
extern void ktime_get_coarse_real_ts64_mg(struct timespec64 *ts);
extern void ktime_get_real_ts64_mg(struct timespec64 *ts);
extern unsigned long timekeeping_get_mg_floor_swaps(void);
void getboottime64(struct timespec64 *ts);

1
kernel/time/timekeeping.c
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@ -2487,6 +2487,7 @@ void ktime_get_real_ts64_mg(struct timespec64 *ts)
if (atomic64_try_cmpxchg(&mg_floor, &old, mono)) {
ts->tv_nsec = 0;
timespec64_add_ns(ts, nsecs);
timekeeping_inc_mg_floor_swaps();
} else {
/*
* Another task changed mg_floor since "old" was fetched.

13
kernel/time/timekeeping_debug.c
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@ -17,6 +17,9 @@
#define NUM_BINS 32
/* Incremented every time mg_floor is updated */
DEFINE_PER_CPU(unsigned long, timekeeping_mg_floor_swaps);
static unsigned int sleep_time_bin[NUM_BINS] = {0};
static int tk_debug_sleep_time_show(struct seq_file *s, void *data)
@ -53,3 +56,13 @@ void tk_debug_account_sleep_time(const struct timespec64 *t)
(s64)t->tv_sec, t->tv_nsec / NSEC_PER_MSEC);
}
unsigned long timekeeping_get_mg_floor_swaps(void)
{
unsigned long sum = 0;
int cpu;
for_each_possible_cpu(cpu)
sum += data_race(per_cpu(timekeeping_mg_floor_swaps, cpu));
return sum;
}

15
kernel/time/timekeeping_internal.h
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@ -10,9 +10,24 @@
* timekeeping debug functions
*/
#ifdef CONFIG_DEBUG_FS
DECLARE_PER_CPU(unsigned long, timekeeping_mg_floor_swaps);
static inline void timekeeping_inc_mg_floor_swaps(void)
{
this_cpu_inc(timekeeping_mg_floor_swaps);
}
extern void tk_debug_account_sleep_time(const struct timespec64 *t);
#else
#define tk_debug_account_sleep_time(x)
static inline void timekeeping_inc_mg_floor_swaps(void)
{
}
#endif
#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE