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Eliminate IVC sync between JIT and Ruby threads (#3799)

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Thanks to Ractor (https://github.com/ruby/ruby/pull/2888 and https://github.com/ruby/ruby/pull/3662),
inline caches support parallel access now.
This commit is contained in:
Takashi Kokubun 2020-11-20 22:18:37 -08:00 • committed by GitHub
parent 4988758e3a
commit 0960f56a1d
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GPG key ID: 4AEE18F83AFDEB23
Notes: git 2020-11-21 15:19:02 +09:00 
Merged-By: k0kubun <takashikkbn@gmail.com>
3 changed files with 15 additions and 122 deletions
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47
mjit.c
View file

@ -27,40 +27,6 @@
#include "mjit_worker.c"
// Copy ISeq's states so that race condition does not happen on compilation.
static void
mjit_copy_job_handler(void *data)
{
mjit_copy_job_t *job = data;
if (stop_worker_p) { // check if mutex is still alive, before calling CRITICAL_SECTION_START.
return;
}
CRITICAL_SECTION_START(3, "in mjit_copy_job_handler");
// Make sure that this job is never executed when:
// 1. job is being modified
// 2. alloca memory inside job is expired
// 3. ISeq is GC-ed
if (job->finish_p) {
CRITICAL_SECTION_FINISH(3, "in mjit_copy_job_handler");
return;
}
else if (job->iseq == NULL) { // ISeq GC notified in mjit_free_iseq
job->finish_p = true;
CRITICAL_SECTION_FINISH(3, "in mjit_copy_job_handler");
return;
}
const struct rb_iseq_constant_body *body = job->iseq->body;
if (job->is_entries) {
memcpy(job->is_entries, body->is_entries, sizeof(union iseq_inline_storage_entry) * body->is_size);
}
job->finish_p = true;
rb_native_cond_broadcast(&mjit_worker_wakeup);
CRITICAL_SECTION_FINISH(3, "in mjit_copy_job_handler");
}
extern int rb_thread_create_mjit_thread(void (*worker_func)(void));
// Return an unique file name in /tmp with PREFIX and SUFFIX and
@ -154,9 +120,6 @@ mjit_free_iseq(const rb_iseq_t *iseq)
return;
CRITICAL_SECTION_START(4, "mjit_free_iseq");
if (mjit_copy_job.iseq == iseq) {
mjit_copy_job.iseq = NULL;
}
if (iseq->body->jit_unit) {
// jit_unit is not freed here because it may be referred by multiple
// lists of units. `get_from_list` and `mjit_finish` do the job.
@ -1050,19 +1013,11 @@ mjit_mark(void)
return;
RUBY_MARK_ENTER("mjit");
CRITICAL_SECTION_START(4, "mjit_mark");
VALUE iseq = (VALUE)mjit_copy_job.iseq;
CRITICAL_SECTION_FINISH(4, "mjit_mark");
// Don't wrap critical section with this. This may trigger GC,
// and in that case mjit_gc_start_hook causes deadlock.
if (iseq) rb_gc_mark(iseq);
struct rb_mjit_unit *unit = NULL;
CRITICAL_SECTION_START(4, "mjit_mark");
list_for_each(&unit_queue.head, unit, unode) {
if (unit->iseq) { // ISeq is still not GCed
iseq = (VALUE)unit->iseq;
VALUE iseq = (VALUE)unit->iseq;
CRITICAL_SECTION_FINISH(4, "mjit_mark rb_gc_mark");
// Don't wrap critical section with this. This may trigger GC,

20
mjit_compile.c
View file

@ -320,8 +320,16 @@ compile_cancel_handler(FILE *f, const struct rb_iseq_constant_body *body, struct
extern int
mjit_capture_cc_entries(const struct rb_iseq_constant_body *compiled_iseq, const struct rb_iseq_constant_body *captured_iseq);
extern bool mjit_copy_cache_from_main_thread(const rb_iseq_t *iseq,
union iseq_inline_storage_entry *is_entries);
// Copy current is_entries and use it throughout the current compilation consistently.
// While ic->entry has been immutable since https://github.com/ruby/ruby/pull/3662,
// we still need this to avoid a race condition between entries and ivar_serial/max_ivar_index.
static void
mjit_capture_is_entries(const struct rb_iseq_constant_body *body, union iseq_inline_storage_entry *is_entries)
{
if (is_entries == NULL)
return;
memcpy(is_entries, body->is_entries, sizeof(union iseq_inline_storage_entry) * body->is_size);
}
static bool
mjit_compile_body(FILE *f, const rb_iseq_t *iseq, struct compile_status *status)
@ -429,6 +437,8 @@ inlinable_iseq_p(const struct rb_iseq_constant_body *body)
static void
init_ivar_compile_status(const struct rb_iseq_constant_body *body, struct compile_status *status)
{
mjit_capture_is_entries(body, status->is_entries);
int num_ivars = 0;
unsigned int pos = 0;
status->max_ivar_index = 0;
@ -528,8 +538,7 @@ precompile_inlinable_iseqs(FILE *f, const rb_iseq_t *iseq, struct compile_status
.param_size = child_iseq->body->param.size,
.local_size = child_iseq->body->local_table_size
};
if ((child_iseq->body->ci_size > 0 && child_status.cc_entries_index == -1)
|| (child_status.is_entries != NULL && !mjit_copy_cache_from_main_thread(child_iseq, child_status.is_entries))) {
if (child_iseq->body->ci_size > 0 && child_status.cc_entries_index == -1) {
return false;
}
init_ivar_compile_status(child_iseq->body, &child_status);
@ -556,8 +565,7 @@ mjit_compile(FILE *f, const rb_iseq_t *iseq, const char *funcname, int id)
{
struct compile_status status = { .compiled_iseq = iseq->body, .compiled_id = id };
INIT_COMPILE_STATUS(status, iseq->body, true);
if ((iseq->body->ci_size > 0 && status.cc_entries_index == -1)
|| (status.is_entries != NULL && !mjit_copy_cache_from_main_thread(iseq, status.is_entries))) {
if (iseq->body->ci_size > 0 && status.cc_entries_index == -1) {
return false;
}
init_ivar_compile_status(iseq->body, &status);

70
mjit_worker.c
View file

@ -1205,21 +1205,6 @@ convert_unit_to_func(struct rb_mjit_unit *unit)
return (mjit_func_t)func;
}
typedef struct {
const rb_iseq_t *iseq;
union iseq_inline_storage_entry *is_entries;
bool finish_p;
} mjit_copy_job_t;
// Singleton MJIT copy job. This is made global since it needs to be durable even when MJIT worker thread is stopped.
// (ex: register job -> MJIT pause -> MJIT resume -> dispatch job. Actually this should be just cancelled by finish_p check)
static mjit_copy_job_t mjit_copy_job = { .iseq = NULL, .finish_p = true };
static void mjit_copy_job_handler(void *data);
// vm_trace.c
int rb_workqueue_register(unsigned flags, rb_postponed_job_func_t , void *);
// To see cc_entries using index returned by `mjit_capture_cc_entries` in mjit_compile.c
const struct rb_callcache **
mjit_iseq_cc_entries(const struct rb_iseq_constant_body *const body)
@ -1266,61 +1251,6 @@ mjit_capture_cc_entries(const struct rb_iseq_constant_body *compiled_iseq, const
return cc_entries_index;
}
// Copy inline cache values of `iseq` to `cc_entries` and `is_entries`.
// These buffers should be pre-allocated properly prior to calling this function.
// Return true if copy succeeds or is not needed.
//
// We're lazily copying cache values from main thread because these cache values
// could be different between ones on enqueue timing and ones on dequeue timing.
bool
mjit_copy_cache_from_main_thread(const rb_iseq_t *iseq, union iseq_inline_storage_entry *is_entries)
{
mjit_copy_job_t *job = &mjit_copy_job; // just a short hand
CRITICAL_SECTION_START(3, "in mjit_copy_cache_from_main_thread");
job->finish_p = true; // disable dispatching this job in mjit_copy_job_handler while it's being modified
CRITICAL_SECTION_FINISH(3, "in mjit_copy_cache_from_main_thread");
job->is_entries = is_entries;
CRITICAL_SECTION_START(3, "in mjit_copy_cache_from_main_thread");
job->iseq = iseq; // Prevernt GC of this ISeq from here
VM_ASSERT(in_jit);
in_jit = false; // To avoid deadlock, allow running GC while waiting for copy job
rb_native_cond_signal(&mjit_client_wakeup); // Unblock main thread waiting in `mjit_gc_start_hook`
job->finish_p = false; // allow dispatching this job in mjit_copy_job_handler
CRITICAL_SECTION_FINISH(3, "in mjit_copy_cache_from_main_thread");
if (UNLIKELY(mjit_opts.wait)) {
mjit_copy_job_handler((void *)job);
}
else if (rb_workqueue_register(0, mjit_copy_job_handler, (void *)job)) {
CRITICAL_SECTION_START(3, "in MJIT copy job wait");
// checking `stop_worker_p` too because `RUBY_VM_CHECK_INTS(ec)` may not
// lush mjit_copy_job_handler when EC_EXEC_TAG() is not TAG_NONE, and then
// `stop_worker()` could dead lock with this function.
while (!job->finish_p && !stop_worker_p) {
rb_native_cond_wait(&mjit_worker_wakeup, &mjit_engine_mutex);
verbose(3, "Getting wakeup from client");
}
CRITICAL_SECTION_FINISH(3, "in MJIT copy job wait");
}
CRITICAL_SECTION_START(3, "in mjit_copy_cache_from_main_thread");
bool success_p = job->finish_p;
// Disable dispatching this job in mjit_copy_job_handler while memory allocated by alloca
// could be expired after finishing this function.
job->finish_p = true;
in_jit = true; // Prohibit GC during JIT compilation
if (job->iseq == NULL) // ISeq GC is notified in mjit_free_iseq
success_p = false;
job->iseq = NULL; // Allow future GC of this ISeq from here
CRITICAL_SECTION_FINISH(3, "in mjit_copy_cache_from_main_thread");
return success_p;
}
// The function implementing a worker. It is executed in a separate
// thread by rb_thread_create_mjit_thread. It compiles precompiled header
// and then compiles requested ISeqs.