executor: optimize waiting for child processes exit

Currently we sleep only for 1 ms, which may produce some excessive CPU load
(we usually have 6/8 such processes waiting).
Make it sleep for 10 ms, but also make the sleep return immediately on child exit.
This shuold both improve latency and reduce CPU load.

3 files changed, 11 insertions, 1 deletions

diff --git a/executor/common.h b/executor/common.h
index fdbf4bcb1..3a735a086 100644
--- a/executor/common.h
+++ b/executor/common.h
@@ -678,9 +678,9 @@ static void loop(void)
 		uint32 executed_calls = __atomic_load_n(output_data, __ATOMIC_RELAXED);
 #endif
 		for (;;) {
+			sleep_ms(10);
 			if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
 				break;
-			sleep_ms(1);
 #if SYZ_EXECUTOR
 			// Even though the test process executes exit at the end
 			// and execution time of each syscall is bounded by syscall_timeout_ms (~50ms),
diff --git a/executor/executor_bsd.h b/executor/executor_bsd.h
index 6c2174360..43c2a19a9 100644
--- a/executor/executor_bsd.h
+++ b/executor/executor_bsd.h
@@ -41,6 +41,11 @@ static void os_init(int argc, char** argv, void* data, size_t data_size)
 	struct rlimit rlim;
 	rlim.rlim_cur = rlim.rlim_max = kMaxFd;
 	setrlimit(RLIMIT_NOFILE, &rlim);
+
+	// A SIGCHLD handler makes sleep in loop exit immediately return with EINTR with a child exits.
+	struct sigaction act = {};
+	act.sa_handler = [](int) {};
+	sigaction(SIGCHLD, &act, nullptr);
 }
 
 static intptr_t execute_syscall(const call_t* c, intptr_t a[kMaxArgs])
diff --git a/executor/executor_linux.h b/executor/executor_linux.h
index 3956127cd..bfd81776f 100644
--- a/executor/executor_linux.h
+++ b/executor/executor_linux.h
@@ -67,6 +67,11 @@ static void os_init(int argc, char** argv, char* data, size_t data_size)
 	got = mmap(data + data_size, SYZ_PAGE_SIZE, PROT_NONE, MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
 	if (data + data_size != got)
 		failmsg("mmap of right data PROT_NONE page failed", "want %p, got %p", data + data_size, got);
+
+	// A SIGCHLD handler makes sleep in loop exit immediately return with EINTR with a child exits.
+	struct sigaction act = {};
+	act.sa_handler = [](int) {};
+	sigaction(SIGCHLD, &act, nullptr);
 }
 
 static intptr_t execute_syscall(const call_t* c, intptr_t a[kMaxArgs])