nproc: Expose processor count and use it to pick between yielding and non-yielding spin locks

apps/nproc.c

@@ -0,0 +1,15 @@
+/**
+ * @brief Print the number of available processors.
+ *
+ * @copyright
+ * This file is part of ToaruOS and is released under the terms
+ * of the NCSA / University of Illinois License - see LICENSE.md
+ * Copyright (C) 2018 K. Lange
+ */
+#include <stdio.h>
+#include <sys/sysfunc.h>
+
+int main(int argc, char * argv[]) {
+	printf("%d\n", sysfunc(TOARU_SYS_FUNC_NPROC, NULL));
+	return 0;
+}

base/usr/include/sys/sysfunc.h

@@ -21,6 +21,7 @@
 #define TOARU_SYS_FUNC_THREADNAME   11
 #define TOARU_SYS_FUNC_SETVGACURSOR 13
 #define TOARU_SYS_FUNC_SETGSBASE    14
+#define TOARU_SYS_FUNC_NPROC        15
 
 _Begin_C_Header
 extern int sysfunc(int command, char ** args);

kernel/sys/syscall.c

@@ -149,6 +149,9 @@ static long sys_sysfunc(long fn, char ** args) {
 			arch_set_tls_base(this_core->current_process->thread.context.tls_base);
 			return 0;
 
+		case TOARU_SYS_FUNC_NPROC:
+			return processor_count;
+
 		default:
 			printf("Bad system function: %ld\n", fn);
 			return -EINVAL;

libc/main.c

@@ -4,6 +4,7 @@
 
 #include <syscall.h>
 #include <syscall_nums.h>
+#include <sys/sysfunc.h>
 
 DEFN_SYSCALL1(exit,  SYS_EXT, int);
 DEFN_SYSCALL2(sleepabs,  SYS_SLEEPABS, unsigned long, unsigned long);
@@ -33,6 +34,7 @@ void _exit(int val){
 
 extern void __make_tls(void);
 
+int __libc_is_multicore = 0;
 static int __libc_init_called = 0;
 
 __attribute__((constructor))
@@ -40,6 +42,7 @@ static void _libc_init(void) {
 	__libc_init_called = 1;
 	__make_tls();
 	__stdio_init_buffers();
+	__libc_is_multicore = sysfunc(TOARU_SYS_FUNC_NPROC, NULL) > 1;
 
 	unsigned int x = 0;
 	unsigned int nulls = 0;

libc/pthread/pthread.c

@@ -17,6 +17,11 @@
 DEFN_SYSCALL3(clone, SYS_CLONE, uintptr_t, uintptr_t, void *);
 DEFN_SYSCALL0(gettid, SYS_GETTID);
 
+extern int __libc_is_multicore;
+static inline void _yield(void) {
+	if (!__libc_is_multicore) syscall_yield();
+}
+
 #define PTHREAD_STACK_SIZE 0x100000
 
 int clone(uintptr_t a,uintptr_t b,void* c) {
@@ -89,7 +94,7 @@ void pthread_cleanup_pop(int execute) {
 
 int pthread_mutex_lock(pthread_mutex_t *mutex) {
 	while (__sync_lock_test_and_set(mutex, 0x01)) {
-		syscall_yield();
+		_yield();
 	}
 	return 0;
 }

libc/pthread/pthread_rwlock.c

@@ -9,7 +9,12 @@
 
 #include <sys/wait.h>
 
-#define ACQUIRE_LOCK() do { while (__sync_lock_test_and_set(&lock->atomic_lock, 0x01)) { syscall_yield(); } } while (0)
+extern int __libc_is_multicore;
+static inline void _yield(void) {
+	if (!__libc_is_multicore) syscall_yield();
+}
+
+#define ACQUIRE_LOCK() do { while (__sync_lock_test_and_set(&lock->atomic_lock, 0x01)) { _yield(); } } while (0)
 #define RELEASE_LOCK() do { __sync_lock_release(&lock->atomic_lock); } while (0)
 
 int pthread_rwlock_init(pthread_rwlock_t * lock, void * args) {
@@ -31,7 +36,7 @@ int pthread_rwlock_wrlock(pthread_rwlock_t * lock) {
 			RELEASE_LOCK();
 			return 0;
 		}
-		syscall_yield();
+		_yield();
 	}
 }
 
@@ -43,7 +48,7 @@ int pthread_rwlock_rdlock(pthread_rwlock_t * lock) {
 			RELEASE_LOCK();
 			return 0;
 		}
-		syscall_yield();
+		_yield();
 	}
 }
 

libc/stdlib/malloc.c

@@ -164,9 +164,15 @@ static void _malloc_assert(const char * file, int line, const char * func, const
 	exit(1);
 }
 
+extern int __libc_is_multicore;
+
+static inline void _yield(void) {
+	if (!__libc_is_multicore) syscall_yield();
+}
+
 static void spin_lock(int volatile * lock, const char * caller) {
 	while(__sync_lock_test_and_set(lock, 0x01)) {
-		syscall_yield();
+		_yield();
 	}
 	_lock_holder = caller;
 }