wingo pushed a commit to branch wip-whippet
in repository guile.
commit d675a9b8f10ccfe49a0633475c6a72bd1876ad1f
Author: Andy Wingo <wi...@igalia.com>
AuthorDate: Tue Feb 11 16:14:27 2025 +0100
Add tracepoints to tracer itself
Also fix an issue whereby the main thread would spin, waiting for other
active threads to finish, doing no work itself.
---
api/gc-lttng.h | 29 +++++++++++++++++----
src/parallel-tracer.h | 71 +++++++++++++++++++++++++++++++--------------------
2 files changed, 68 insertions(+), 32 deletions(-)
diff --git a/api/gc-lttng.h b/api/gc-lttng.h
index 630e7c543..9df639b7d 100644
--- a/api/gc-lttng.h
+++ b/api/gc-lttng.h
@@ -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 */
diff --git a/src/parallel-tracer.h b/src/parallel-tracer.h
index 8115c369d..e368c36d6 100644
--- a/src/parallel-tracer.h
+++ b/src/parallel-tracer.h
@@ -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;
@@ -235,40 +238,45 @@ 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) {
- // 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).
- size_t locked = 1;
- while (locked < tracer->worker_count) {
- if (pthread_mutex_trylock(&tracer->workers[locked].lock) == 0)
- locked++;
- else
- break;
- }
- int done = (locked == tracer->worker_count) &&
- !trace_worker_can_steal_from_any(worker, tracer);
- 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);
+ 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)
+ locked++;
+ else
+ break;
}
+ 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);
+
+ 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");
