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Add tracepoints to tracer itself

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Also fix an issue whereby the main thread would spin, waiting for other
active threads to finish, doing no work itself.
This commit is contained in:
Andy Wingo 2025-02-11 16:14:27 +01:00
parent 461efa98a0
commit d675a9b8f1
2 changed files with 68 additions and 32 deletions
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29
api/gc-lttng.h
View file

@ -72,11 +72,30 @@ LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, mutator_removed, LTTNG_UST_TP_ARGS())
/*
* Use LTTNG_UST_TRACEPOINT_EVENT(), LTTNG_UST_TRACEPOINT_EVENT_CLASS(),
* LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(), and
* LTTNG_UST_TRACEPOINT_LOGLEVEL() here.
*/
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_unpark_all, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_share, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_check_termination_begin, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_check_termination_end, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_steal_begin, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_steal_end, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_roots_begin, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_roots_end, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_objects_begin, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_objects_end, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_worker_begin, LTTNG_UST_TP_ARGS())
LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(
whippet, tracepoint, whippet, trace_worker_end, LTTNG_UST_TP_ARGS())
#endif /* _TP_H */

39
src/parallel-tracer.h
View file

@ -9,6 +9,7 @@
#include "assert.h"
#include "debug.h"
#include "gc-inline.h"
#include "gc-tracepoint.h"
#include "local-worklist.h"
#include "root-worklist.h"
#include "shared-worklist.h"
@ -157,6 +158,7 @@ tracer_unpark_all_workers(struct gc_tracer *tracer) {
long epoch = old_epoch + 1;
DEBUG("starting trace; %zu workers; epoch=%ld\n", tracer->worker_count,
epoch);
GC_TRACEPOINT(trace_unpark_all);
pthread_cond_broadcast(&tracer->cond);
}
@ -171,6 +173,7 @@ tracer_maybe_unpark_workers(struct gc_tracer *tracer) {
static inline void
tracer_share(struct gc_trace_worker *worker) {
DEBUG("tracer #%zu: sharing\n", worker->id);
GC_TRACEPOINT(trace_share);
size_t to_share = LOCAL_WORKLIST_SHARE_AMOUNT;
while (to_share) {
struct gc_ref *objv;
@ -235,21 +238,26 @@ trace_worker_can_steal_from_any(struct gc_trace_worker *worker,
return 0;
}
static int
trace_worker_should_continue(struct gc_trace_worker *worker) {
static size_t
trace_worker_should_continue(struct gc_trace_worker *worker, size_t spin_count) {
// Helper workers should park themselves immediately if they have no work.
if (worker->id != 0)
return 0;
struct gc_tracer *tracer = worker->tracer;
for (size_t spin_count = 0;; spin_count++) {
if (atomic_load_explicit(&tracer->active_tracers,
memory_order_acquire) == 1) {
if (atomic_load_explicit(&tracer->active_tracers, memory_order_acquire) != 1) {
LOG("checking for termination: tracers active, spinning #%zu\n", spin_count);
yield_for_spin(spin_count);
return 1;
}
// All trace workers have exited except us, the main worker. We are
// probably done, but we need to synchronize to be sure that there is no
// work pending, for example if a worker had a spurious wakeup. Skip
// worker 0 (the main worker).
GC_TRACEPOINT(trace_check_termination_begin);
size_t locked = 1;
while (locked < tracer->worker_count) {
if (pthread_mutex_trylock(&tracer->workers[locked].lock) == 0)
@ -259,16 +267,16 @@ trace_worker_should_continue(struct gc_trace_worker *worker) {
}
int done = (locked == tracer->worker_count) &&
!trace_worker_can_steal_from_any(worker, tracer);
GC_TRACEPOINT(trace_check_termination_end);
if (done)
return 0;
while (locked > 1)
pthread_mutex_unlock(&tracer->workers[--locked].lock);
return 1;
}
// spin
LOG("checking for termination: spinning #%zu\n", spin_count);
LOG("checking for termination: failed to lock, spinning #%zu\n", spin_count);
yield_for_spin(spin_count);
}
return 1;
}
static struct gc_ref
@ -285,8 +293,10 @@ trace_worker_steal(struct gc_trace_worker *worker) {
return obj;
}
GC_TRACEPOINT(trace_steal_begin);
LOG("tracer #%zu: trying to steal\n", worker->id);
struct gc_ref obj = trace_worker_steal_from_any(worker, tracer);
GC_TRACEPOINT(trace_steal_end);
if (!gc_ref_is_null(obj))
return obj;
@ -329,7 +339,9 @@ trace_with_data(struct gc_tracer *tracer,
}
} else {
DEBUG("tracer #%zu: tracing objects\n", worker->id);
GC_TRACEPOINT(trace_objects_begin);
size_t n = 0;
size_t spin_count = 0;
do {
while (1) {
struct gc_ref ref;
@ -343,7 +355,8 @@ trace_with_data(struct gc_tracer *tracer,
trace_one(ref, heap, worker);
n++;
}
} while (trace_worker_should_continue(worker));
} while (trace_worker_should_continue(worker, spin_count++));
GC_TRACEPOINT(trace_objects_end);
DEBUG("tracer #%zu: done tracing, %zu objects traced\n", worker->id, n);
}
@ -354,8 +367,10 @@ trace_with_data(struct gc_tracer *tracer,
static void
trace_worker_trace(struct gc_trace_worker *worker) {
GC_TRACEPOINT(trace_worker_begin);
gc_trace_worker_call_with_data(trace_with_data, worker->tracer,
worker->heap, worker);
GC_TRACEPOINT(trace_worker_end);
}
static inline int
@ -406,9 +421,11 @@ static inline void
gc_tracer_trace_roots(struct gc_tracer *tracer) {
DEBUG("starting roots-only trace\n");
GC_TRACEPOINT(trace_roots_begin);
tracer->trace_roots_only = 1;
gc_tracer_trace(tracer);
tracer->trace_roots_only = 0;
GC_TRACEPOINT(trace_roots_end);
GC_ASSERT_EQ(atomic_load(&tracer->active_tracers), 0);
DEBUG("roots-only trace finished\n");