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Do not stop the world during JIT compaction 

Running C compiler for JIT compaction inside a critical section may lock
main thread for a long time when it triggers GC. As I'm planning to
increase this duration a bit, I'd like to make sure this doesn't stop
the world.

For now, I chose to give up unloading units when it's during JIT
compaction, assuming other calls may unload them later.
This commit is contained in:
Takashi Kokubun 2020-04-30 21:37:55 -07:00
parent 520ac5da22
commit e8a78d7df8
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GPG Key ID: 6FFC433B12EE23DD
3 changed files with 25 additions and 17 deletions
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14
mjit.c
View File

@ -362,11 +362,7 @@ unload_units(void)
free_unit(worst);
}
if (units_num == active_units.length && mjit_opts.wait) {
mjit_opts.max_cache_size++; // avoid infinite loop on `rb_mjit_wait_call`. Note that --jit-wait is just for testing.
verbose(1, "No units can be unloaded -- incremented max-cache-size to %d for --jit-wait", mjit_opts.max_cache_size);
}
else {
if (units_num > active_units.length) {
verbose(1, "Too many JIT code -- %d units unloaded", units_num - active_units.length);
}
}
@ -389,9 +385,17 @@ mjit_add_iseq_to_process(const rb_iseq_t *iseq, const struct rb_mjit_compile_inf
CRITICAL_SECTION_START(3, "in add_iseq_to_process");
add_to_list(iseq->body->jit_unit, &unit_queue);
if (active_units.length >= mjit_opts.max_cache_size) {
if (in_compact) {
verbose(1, "Too many JIT code, but skipped unloading units for JIT compaction");
} else {
RB_DEBUG_COUNTER_INC(mjit_unload_units);
unload_units();
}
if (active_units.length == mjit_opts.max_cache_size && mjit_opts.wait) { // Sometimes all methods may be in use
mjit_opts.max_cache_size++; // avoid infinite loop on `rb_mjit_wait_call`. Note that --jit-wait is just for testing.
verbose(1, "No units can be unloaded -- incremented max-cache-size to %d for --jit-wait", mjit_opts.max_cache_size);
}
}
verbose(3, "Sending wakeup signal to workers in mjit_add_iseq_to_process");
rb_native_cond_broadcast(&mjit_worker_wakeup);
CRITICAL_SECTION_FINISH(3, "in add_iseq_to_process");

18
mjit_worker.c
View File

@ -221,9 +221,11 @@ static rb_nativethread_cond_t mjit_worker_wakeup;
// A thread conditional to wake up workers if at the end of GC.
static rb_nativethread_cond_t mjit_gc_wakeup;
// True when GC is working.
static bool in_gc;
static bool in_gc = false;
// True when JIT is working.
static bool in_jit;
static bool in_jit = false;
// True when JIT compaction is running.
static bool in_compact = false;
// Set to true to stop worker.
static bool stop_worker_p;
// Set to true if worker is stopped.
@ -913,21 +915,21 @@ compact_all_jit_code(void)
// NULL-ending for form_args
o_files = alloca(sizeof(char *) * (active_units.length + 1));
o_files[active_units.length] = NULL;
CRITICAL_SECTION_START(3, "in compact_all_jit_code to keep .o files");
CRITICAL_SECTION_START(3, "in compact_all_jit_code to guard .o files from unload_units");
list_for_each(&active_units.head, cur, unode) {
o_files[i] = cur->o_file;
i++;
}
in_compact = true;
CRITICAL_SECTION_FINISH(3, "in compact_all_jit_code to guard .o files from unload_units");
start_time = real_ms_time();
bool success = link_o_to_so(o_files, so_file);
end_time = real_ms_time();
// TODO: Shrink this big critical section. For now, this is needed to prevent failure by missing .o files.
// This assumes that o -> so link doesn't take long time because the bottleneck, which is compiler optimization,
// is already done. But actually it takes about 500ms for 5,000 methods on my Linux machine, so it's better to
// finish this critical section before link_o_to_so by disabling unload_units.
CRITICAL_SECTION_FINISH(3, "in compact_all_jit_code to keep .o files");
CRITICAL_SECTION_START(3, "in compact_all_jit_code to release .o files");
in_compact = false;
CRITICAL_SECTION_FINISH(3, "in compact_all_jit_code to release .o files");
if (success) {
void *handle = dlopen(so_file, RTLD_NOW);

6
test/ruby/test_jit.rb
View File

@ -14,6 +14,7 @@ class TestJIT < Test::Unit::TestCase
]
MAX_CACHE_PATTERNS = [
/\AJIT compaction \([^)]+\): .+\n\z/,
/\AToo many JIT code, but skipped unloading units for JIT compaction\n\z/,
/\ANo units can be unloaded -- .+\n\z/,
]
@ -700,8 +701,9 @@ class TestJIT < Test::Unit::TestCase
10.times do |i|
assert_match(/\A#{JIT_SUCCESS_PREFIX}: mjit#{i}@\(eval\):/, errs[i], debug_info)
end
assert_equal("Too many JIT code -- 1 units unloaded\n", errs[10], debug_info)
assert_match(/\A#{JIT_SUCCESS_PREFIX}: mjit10@\(eval\):/, errs[11], debug_info)
assert_equal("Too many JIT code, but skipped unloading units for JIT compaction\n", errs[10], debug_info)
assert_equal("No units can be unloaded -- incremented max-cache-size to 11 for --jit-wait\n", errs[11], debug_info)
assert_match(/\A#{JIT_SUCCESS_PREFIX}: mjit10@\(eval\):/, errs[12], debug_info)
# On --jit-wait, when the number of JIT-ed code reaches --jit-max-cache,
# it should trigger compaction.