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fiber.top() refactor clock and cpu time calculation
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Unify all the members related to fiber's clock statistics into struct
clock_stat and all the members related to cord's knowledge of cpu state
and clocks to struct cpu_stat.
Reset stats of all alive fibers on fiber.top_enable().

Follow-up #2694
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@sergepetrenko
sergepetrenko committed Nov 18, 2019
1 parent 8d363c4 commit 9acb94c
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Showing 3 changed files with 199 additions and 109 deletions.
179 changes: 109 additions & 70 deletions src/lib/core/fiber.c
View file
Expand Up @@ -88,6 +88,9 @@ static int (*fiber_invoke)(fiber_func f, va_list ap);

#if ENABLE_FIBER_TOP
static __thread bool fiber_top_enabled = false;

uint64_t
cpu_stat_on_csw(struct cpu_stat *stat);
#endif /* ENABLE_FIBER_TOP */

/**
Expand All @@ -103,18 +106,10 @@ clock_set_on_csw(struct fiber *caller)
if (!fiber_top_enabled)
return;

uint64_t clock;
uint32_t cpu_id;
clock = __rdtscp(&cpu_id);
uint64_t delta = cpu_stat_on_csw(&cord()->cpu_stat);

if (cpu_id == cord()->cpu_id_last) {
caller->clock_delta += clock - cord()->clock_last;
cord()->clock_delta += clock - cord()->clock_last;
} else {
cord()->cpu_id_last = cpu_id;
cord()->cpu_miss_count++;
}
cord()->clock_last = clock;
clock_stat_add_delta(&cord()->clock_stat, delta);
clock_stat_add_delta(&caller->clock_stat, delta);
#endif /* ENABLE_FIBER_TOP */

}
Expand Down Expand Up @@ -695,9 +690,7 @@ fiber_reset(struct fiber *fiber)
rlist_create(&fiber->on_stop);
fiber->flags = FIBER_DEFAULT_FLAGS;
#if ENABLE_FIBER_TOP
fiber->cputime = 0;
fiber->clock_acc = 0;
fiber->clock_delta = 0;
clock_stat_reset(&fiber->clock_stat);
#endif /* ENABLE_FIBER_TOP */
}

Expand Down Expand Up @@ -1095,9 +1088,52 @@ loop_on_iteration_start(ev_loop *loop, ev_check *watcher, int revents)
(void) watcher;
(void) revents;

cord()->clock_last = __rdtscp(&cord()->cpu_id_last);
cord()->cpu_miss_count = 0;
cpu_stat_start(&cord()->cpu_stat);
}

/**
* Calculate the exponential moving average for the clock deltas
* per loop iteration. The coeffitient is 1/16.
*/
static inline uint64_t
clock_diff_accumulate(uint64_t acc, uint64_t delta)
{
if (acc > 0) {
return delta / 16 + 15 * acc / 16;
} else {
return delta;
}
}

inline void
clock_stat_add_delta(struct clock_stat *stat, uint64_t clock_delta)
{
stat->delta += clock_delta;
}

void
clock_stat_update(struct clock_stat *stat, double nsec_per_clock)
{
stat->acc = clock_diff_accumulate(stat->acc, stat->delta);
stat->prev_delta = stat->delta;
stat->cputime += stat->delta * nsec_per_clock;
stat->delta = 0;
}

void
clock_stat_reset(struct clock_stat *stat)
{
stat->acc = 0;
stat->delta = 0;
stat->prev_delta = 0;
stat->cputime = 0;
}

void
cpu_stat_start(struct cpu_stat *stat)
{
stat->prev_clock = __rdtscp(&stat->prev_cpu_id);
stat->cpu_miss_count = 0;
/*
* We want to measure thread cpu time here to calculate
* each fiber's cpu time, so don't use libev's ev_now() or
Expand All @@ -1106,27 +1142,59 @@ loop_on_iteration_start(ev_loop *loop, ev_check *watcher, int revents)
*/
struct timespec ts;
if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0) {
say_debug("clock_gettime(): failed to get this"
"thread's cpu time.");
say_debug("clock_gettime(): failed to get this thread's"
" cpu time.");
return;
}
cord()->cputime_last = (uint64_t) ts.tv_sec * FIBER_TIME_RES +
ts.tv_nsec;
stat->prev_cputime = (uint64_t) ts.tv_sec * FIBER_TIME_RES + ts.tv_nsec;
}

void
cpu_stat_reset(struct cpu_stat *stat)
{
stat->prev_cpu_miss_count = 0;
cpu_stat_start(stat);
}

/**
* Calculate the exponential moving average for the clock deltas
* per loop iteration. The coeffitient is 1/16.
*/
static inline uint64_t
clock_diff_accumulate(uint64_t acc, uint64_t delta)
uint64_t
cpu_stat_on_csw(struct cpu_stat *stat)
{
if (acc > 0) {
return delta / 16 + 15 * acc / 16;
uint32_t cpu_id;
uint64_t delta = 0;
uint64_t clock = __rdtscp(&cpu_id);

if (cpu_id == stat->prev_cpu_id) {
delta = clock - stat->prev_clock;
} else {
return delta;
stat->prev_cpu_id = cpu_id;
stat->cpu_miss_count++;
}
stat->prev_clock = clock;

return delta;
}

double
cpu_stat_end(struct cpu_stat *stat, struct clock_stat *cord_clock_stat)
{
stat->prev_cpu_miss_count = stat->cpu_miss_count;
stat->cpu_miss_count = 0;

struct timespec ts;
uint64_t delta_time;
double nsec_per_clock = 0;
if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0) {
say_debug("clock_gettime(): failed to get this thread's"
" cpu time.");
} else {
delta_time = (uint64_t) ts.tv_sec * FIBER_TIME_RES +
ts.tv_nsec;
if (delta_time > stat->prev_cputime && cord_clock_stat->delta > 0) {
delta_time -= stat->prev_cputime;
nsec_per_clock = (double) delta_time / cord()->clock_stat.delta;
}
}
return nsec_per_clock;
}

static void
Expand All @@ -1145,40 +1213,14 @@ loop_on_iteration_end(ev_loop *loop, ev_prepare *watcher, int revents)
*/
clock_set_on_csw(&cord()->sched);

cord()->cpu_miss_count_last = cord()->cpu_miss_count;
cord()->cpu_miss_count = 0;
double nsec_per_clock = cpu_stat_end(&cord()->cpu_stat,
&cord()->clock_stat);

struct timespec ts;
uint64_t delta_time;
double nsec_per_clock = 0;

if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0) {
say_debug("clock_gettime(): failed to get this"
"thread's cpu time.");
} else {
delta_time = (uint64_t) ts.tv_sec * FIBER_TIME_RES +
ts.tv_nsec;
assert(delta_time > cord()->cputime_last);
delta_time -= cord()->cputime_last;

if (cord()->clock_delta > 0)
nsec_per_clock = (double) delta_time / cord()->clock_delta;
}

cord()->clock_acc = clock_diff_accumulate(cord()->clock_acc, cord()->clock_delta);
cord()->clock_delta_last = cord()->clock_delta;
cord()->clock_delta = 0;

cord()->sched.clock_acc = clock_diff_accumulate(cord()->sched.clock_acc, cord()->sched.clock_delta);
cord()->sched.clock_delta_last = cord()->sched.clock_delta;
cord()->sched.cputime += cord()->sched.clock_delta * nsec_per_clock;
cord()->sched.clock_delta = 0;
clock_stat_update(&cord()->clock_stat, nsec_per_clock);
clock_stat_update(&cord()->sched.clock_stat, nsec_per_clock);

rlist_foreach_entry(fiber, &cord()->alive, link) {
fiber->clock_acc = clock_diff_accumulate(fiber->clock_acc, fiber->clock_delta);
fiber->clock_delta_last = fiber->clock_delta;
fiber->cputime += fiber->clock_delta * nsec_per_clock;
fiber->clock_delta = 0;
clock_stat_update(&fiber->clock_stat, nsec_per_clock);
}
}

Expand All @@ -1203,17 +1245,14 @@ fiber_top_enable()
ev_check_start(cord()->loop, &cord()->check_event);
fiber_top_enabled = true;

cord()->clock_acc = 0;
cord()->cpu_miss_count_last = 0;
cord()->clock_delta_last = 0;
struct timespec ts;
if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0) {
say_debug("clock_gettime(): failed to get this"
"thread's cpu time.");
return;
cpu_stat_reset(&cord()->cpu_stat);
clock_stat_reset(&cord()->clock_stat);
clock_stat_reset(&cord()->sched.clock_stat);

struct fiber *fiber;
rlist_foreach_entry(fiber, &cord()->alive, link) {
clock_stat_reset(&fiber->clock_stat);
}
cord()->cputime_last = (uint64_t) ts.tv_sec * FIBER_TIME_RES +
ts.tv_nsec;
}
}

Expand Down
109 changes: 75 additions & 34 deletions src/lib/core/fiber.h
View file
Expand Up @@ -56,14 +56,82 @@
#define ENABLE_FIBER_TOP 1
#endif

#if defined(__cplusplus)
extern "C" {
#endif /* defined(__cplusplus) */

#if ENABLE_FIBER_TOP
/* A fiber reports used up CPU time with nanosecond resolution. */
#define FIBER_TIME_RES 1000000000
#endif /* ENABLE_FIBER_TOP */

#if defined(__cplusplus)
extern "C" {
#endif /* defined(__cplusplus) */
/**
* A struct containing all the info gathered for current fiber or
* thread as a whole when fiber.top() is enabled.
*/
struct clock_stat {
/**
* Accumulated clock value calculated using exponential
* moving average.
*/
uint64_t acc;
/**
* Clock delta counter used on current event loop
* iteration.
*/
uint64_t delta;
/**
* Clock delta calculated on previous event loop
* iteration.
*/
uint64_t prev_delta;
/**
* Total processor time this fiber (or cord as a whole)
* has spent with 1 / FIBER_TIME_RES second precision.
*/
uint64_t cputime;
};

void
clock_stat_add_delta(struct clock_stat *stat, uint64_t clock_delta);

void
clock_stat_update(struct clock_stat *stat, double nsec_per_clock);

void
clock_stat_reset(struct clock_stat *stat);

/**
* A struct encapsulating all knowledge this cord has about cpu
* clocks and their state.
*/
struct cpu_stat {
uint64_t prev_clock;
/**
* This thread's CPU time at the beginning of event loop
* iteration. Used to calculate how much cpu time has
* each loop iteration consumed and update fiber cpu
* times propotionally. The resolution is
* 1 / FIBER_TIME_RES seconds.
*/
uint64_t prev_cputime;
uint32_t prev_cpu_id;
uint32_t cpu_miss_count;
uint32_t prev_cpu_miss_count;
};

void
cpu_stat_start(struct cpu_stat *stat);

void
cpu_stat_reset(struct cpu_stat *stat);

uint64_t
cpu_stat_on_csw(struct cpu_stat *stat);

double
cpu_stat_end(struct cpu_stat *stat, struct clock_stat *cord_clock_stat);

#endif /* ENABLE_FIBER_TOP */

enum { FIBER_NAME_MAX = 32 };

Expand Down Expand Up @@ -402,21 +470,7 @@ struct fiber {
/** Fiber flags */
uint32_t flags;
#if ENABLE_FIBER_TOP
/**
* Accumulated clock value calculated using exponential
* moving average.
*/
uint64_t clock_acc;
/**
* Total processor time this fiber has spent with
* 1 / FIBER_TIME_RES second precision.
*/
uint64_t cputime;
/**
* Clock delta calculated on previous event loop iteration.
*/
uint64_t clock_delta_last;
uint64_t clock_delta;
struct clock_stat clock_stat;
#endif /* ENABLE_FIBER_TOP */
/** Link in cord->alive or cord->dead list. */
struct rlist link;
Expand Down Expand Up @@ -490,21 +544,8 @@ struct cord {
*/
uint32_t max_fid;
#if ENABLE_FIBER_TOP
uint64_t clock_acc;
uint64_t clock_delta;
uint64_t clock_delta_last;
uint64_t clock_last;
uint32_t cpu_id_last;
uint32_t cpu_miss_count;
uint32_t cpu_miss_count_last;
/**
* This thread's CPU time at the beginning of event loop
* iteration. Used to calculate how much cpu time has
* each loop iteration consumed and update fiber cpu
* times propotionally. The resolution is
* 1 / FIBER_TIME_RES seconds.
*/
uint64_t cputime_last;
struct clock_stat clock_stat;
struct cpu_stat cpu_stat;
#endif /* ENABLE_FIBER_TOP */
pthread_t id;
const struct cord_on_exit *on_exit;
Expand Down

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