gettimeofday: avoid per-cpu data in calculation

Because it is difficult to safely update per-cpu data of other cpus in
settimeofday().

kernel/include/cls.h

@@ -73,11 +73,6 @@ struct cpu_local_var {
 	int in_interrupt;
 	int no_preempt;
 	int timer_enabled;
-
-	unsigned long tv_sec;
-	unsigned long tv_nsec;
-	unsigned long last_tsc;
-
 } __attribute__((aligned(64)));
 
 

kernel/include/syscall.h

@@ -16,6 +16,7 @@
 #include <ihk/context.h>
 #include <ihk/memconst.h>
 #include <rlimit.h>
+#include <time.h>
 
 #define NUM_SYSCALLS 255
 
@@ -286,4 +287,9 @@ struct procfs_file {
 };
 
 extern void terminate(int, int);
+
+/* kernel/syscall.c */
+extern struct timespec origin_ts;		/* realtime when tsc=0 */
+extern unsigned long clocks_per_sec;
+
 #endif

kernel/init.c

@@ -201,11 +201,21 @@ static void pc_test(void)
 }
 
 extern void ihk_mc_get_boot_time(unsigned long *tv_sec, unsigned long *tv_nsec);
+extern unsigned long ihk_mc_get_ns_per_tsc(void);
+
 static void time_init(void)
 {
-	ihk_mc_get_boot_time(&cpu_local_var(tv_sec),
-		&cpu_local_var(tv_nsec));
-	cpu_local_var(last_tsc) = 0;
+	unsigned long tv_sec, tv_nsec;
+	unsigned long ns_per_kclock;
+
+	ihk_mc_get_boot_time(&tv_sec, &tv_nsec);
+	ns_per_kclock = ihk_mc_get_ns_per_tsc();
+
+	origin_ts.tv_sec = tv_sec;
+	origin_ts.tv_nsec = tv_nsec;
+	clocks_per_sec = (1000L * NS_PER_SEC) / ns_per_kclock;
+
+	return;
 }
 
 static void rest_init(void)
@@ -233,11 +243,9 @@ static void rest_init(void)
 int host_ikc_inited = 0;
 extern int num_processors;
 extern void zero_tsc(void);
-extern void update_cpu_local_time(void);
 
 static void post_init(void)
 {
-	int i;
 	cpu_enable_interrupt();
 
 	while (!host_ikc_inited) {
@@ -253,16 +261,9 @@ static void post_init(void)
 		ihk_mc_spinlock_init(&syscall_lock);
 	}
 
-	/* Update time elapsed so far during boot, distribute the current
-	 * date to all cores and zero TSC.
+	/* Zero TSC.
 	 * All AP cores are wait spinning for ap_start() and they will zero
 	 * their TSC immediatly. */
-	update_cpu_local_time();
-	cpu_local_var(last_tsc) = 0;
-	for (i = 0; i < num_processors; ++i) {
-		get_cpu_local_var(i)->tv_sec = cpu_local_var(tv_sec);
-		get_cpu_local_var(i)->tv_nsec = cpu_local_var(tv_nsec);
-	}
 	zero_tsc();
 	ap_start();
 

kernel/syscall.c

@@ -94,6 +94,9 @@ static char *syscall_name[] MCKERNEL_UNUSED = {
 #undef	SYSCALL_DELEGATED
 };
 
+struct timespec origin_ts;
+unsigned long clocks_per_sec;
+
 void check_signal(unsigned long, void *, int);
 void do_signal(long rc, void *regs, struct thread *thread, struct sig_pending *pending, int num);
 extern unsigned long do_kill(struct thread *thread, int pid, int tid, int sig, struct siginfo *info, int ptracecont);
@@ -4786,30 +4789,26 @@ SYSCALL_DECLARE(get_cpu_id)
 	return ihk_mc_get_processor_id();
 }
 
-void __update_time_from_tsc_delta(unsigned long *tv_sec,
-	unsigned long *tv_nsec,
-	unsigned long tsc_delta)
+static void calculate_time_from_tsc(struct timespec *ts)
 {
-	unsigned long ns_delta = tsc_delta * ihk_mc_get_ns_per_tsc() / 1000;
+	unsigned long current_tsc;
+	time_t sec_delta;
+	long ns_delta;
 
-	*tv_sec += (ns_delta / NS_PER_SEC);
-	*tv_nsec += (ns_delta % NS_PER_SEC);
-	if (*tv_nsec > NS_PER_SEC) {
-		*tv_nsec -= NS_PER_SEC;
-		++*tv_sec;
+	current_tsc = rdtsc();
+	sec_delta = current_tsc / clocks_per_sec;
+	ns_delta = NS_PER_SEC * (current_tsc % clocks_per_sec)
+		/ clocks_per_sec;
+	/* calc. of ns_delta overflows if clocks_per_sec exceeds 18.44 GHz */
+
+	ts->tv_sec = origin_ts.tv_sec + sec_delta;
+	ts->tv_nsec = origin_ts.tv_nsec + ns_delta;
+	if (ts->tv_nsec >= NS_PER_SEC) {
+		ts->tv_nsec -= NS_PER_SEC;
+		++ts->tv_sec;
 	}
-}
 
-void update_cpu_local_time(void)
-{
-	unsigned long tsc = rdtsc();
-
-	__update_time_from_tsc_delta(
-		&cpu_local_var(tv_sec),
-		&cpu_local_var(tv_nsec),
-		tsc - cpu_local_var(last_tsc));
-
-	cpu_local_var(last_tsc) = tsc;
+	return;
 }
 
 
@@ -4820,6 +4819,7 @@ SYSCALL_DECLARE(gettimeofday)
 	struct timezone *tz = (struct timezone *)ihk_mc_syscall_arg1(ctx);
 	struct timeval atv;
 	int error;
+	struct timespec ats;
 
 	if (!tv && !tz) {
 		/* nothing to do */
@@ -4828,10 +4828,10 @@ SYSCALL_DECLARE(gettimeofday)
 
 	/* Do it locally if supported */
 	if (!tz && gettime_local_support) {
-		update_cpu_local_time();
+		calculate_time_from_tsc(&ats);
 
-		atv.tv_sec = cpu_local_var(tv_sec);
-		atv.tv_usec = cpu_local_var(tv_nsec) / 1000;
+		atv.tv_sec = ats.tv_sec;
+		atv.tv_usec = ats.tv_nsec / 1000;
 
 		error = copy_to_user(tv, &atv, sizeof(atv));