vsyscall_gettimeofday: make timeval from TSC

arch/x86/kernel/vsyscall.c

@@ -18,14 +18,84 @@
  */
 
 #include <syscall.h>
+#include <ihk/atomic.h>
+#include <arch/cpu.h>
 
-extern int vsyscall_gettimeofday(void *tv, void *tz)
+extern int vsyscall_gettimeofday(struct timeval *tv, void *tz)
 	__attribute__ ((section (".vsyscall.gettimeofday")));
 
-int vsyscall_gettimeofday(void *tv, void *tz)
+struct tod_data_s tod_data
+		__attribute__ ((section(".vsyscall.gettimeofday.data"))) = {
+	.do_local =	0,
+	.version =	IHK_ATOMIC64_INIT(0),
+};
+
+static inline void cpu_pause_for_vsyscall(void)
+{
+	asm volatile ("pause" ::: "memory");
+	return;
+} /* cpu_pause_for_vsyscall() */
+
+static inline void calculate_time_from_tsc(struct timespec *ts)
+{
+	long ver;
+	unsigned long current_tsc;
+	__time_t sec_delta;
+	long ns_delta;
+
+	for (;;) {
+		while ((ver = ihk_atomic64_read(&tod_data.version)) & 1) {
+			/* settimeofday() is in progress */
+			cpu_pause_for_vsyscall();
+		}
+		rmb();
+		*ts = tod_data.origin;
+		rmb();
+		if (ver == ihk_atomic64_read(&tod_data.version)) {
+			break;
+		}
+
+		/* settimeofday() has intervened */
+		cpu_pause_for_vsyscall();
+	}
+
+	current_tsc = rdtsc();
+	sec_delta = current_tsc / tod_data.clocks_per_sec;
+	ns_delta = NS_PER_SEC * (current_tsc % tod_data.clocks_per_sec)
+		/ tod_data.clocks_per_sec;
+	/* calc. of ns_delta overflows if clocks_per_sec exceeds 18.44 GHz */
+
+	ts->tv_sec += sec_delta;
+	ts->tv_nsec += ns_delta;
+	if (ts->tv_nsec >= NS_PER_SEC) {
+		ts->tv_nsec -= NS_PER_SEC;
+		++ts->tv_sec;
+	}
+
+	return;
+} /* calculate_time_from_tsc() */
+
+int vsyscall_gettimeofday(struct timeval *tv, void *tz)
 {
 	int error;
+	struct timespec ats;
 
+	if (!tv && !tz) {
+		/* nothing to do */
+		return 0;
+	}
+
+	/* Do it locally if supported */
+	if (!tz && tod_data.do_local) {
+		calculate_time_from_tsc(&ats);
+
+		tv->tv_sec = ats.tv_sec;
+		tv->tv_usec = ats.tv_nsec / 1000;
+
+		return 0;
+	}
+
+	/* Otherwise syscall */
 	asm ("syscall" : "=a" (error)
 			: "a" (__NR_gettimeofday), "D" (tv), "S" (tz)
 			: "%rcx", "%r11", "memory");
@@ -34,7 +104,7 @@ int vsyscall_gettimeofday(void *tv, void *tz)
 		*(int *)0 = 0;	/* i.e. raise(SIGSEGV) */
 	}
 	return error;
-}
+} /* vsyscall_gettimeofday() */
 
 extern long vsyscall_time(void *tp)
 	__attribute__ ((section (".vsyscall.time")));

kernel/config/attached-mic.lds

@@ -26,6 +26,7 @@ SECTIONS
 
 		. = vsyscall_page + 0x000;
 		*(.vsyscall.gettimeofday)
+		*(.vsyscall.gettimeofday.*)
 
 		. = vsyscall_page + 0x400;
 		*(.vsyscall.time)

kernel/config/builtin-mic.lds

@@ -26,6 +26,7 @@ SECTIONS
 
 		. = vsyscall_page + 0x000;
 		*(.vsyscall.gettimeofday)
+		*(.vsyscall.gettimeofday.*)
 
 		. = vsyscall_page + 0x400;
 		*(.vsyscall.time)

kernel/config/builtin-x86.lds

@@ -26,6 +26,7 @@ SECTIONS
 
 		. = vsyscall_page + 0x000;
 		*(.vsyscall.gettimeofday)
+		*(.vsyscall.gettimeofday.*)
 
 		. = vsyscall_page + 0x400;
 		*(.vsyscall.time)

kernel/config/smp-x86.lds

@@ -26,6 +26,7 @@ SECTIONS
 
 		. = vsyscall_page + 0x000;
 		*(.vsyscall.gettimeofday)
+		*(.vsyscall.gettimeofday.*)
 
 		. = vsyscall_page + 0x400;
 		*(.vsyscall.time)

kernel/include/syscall.h

@@ -296,6 +296,6 @@ struct tod_data_s {
 	unsigned long clocks_per_sec;
 	struct timespec origin;		/* realtime when tsc=0 */
 };
-extern struct tod_data_s tod_data;
+extern struct tod_data_s tod_data;	/* residing in arch-dependent file */
 
 #endif

kernel/syscall.c

@@ -95,10 +95,6 @@ static char *syscall_name[] MCKERNEL_UNUSED = {
 #undef	SYSCALL_DELEGATED
 };
 
-struct tod_data_s tod_data = {
-	.do_local =	0,
-	.version =	IHK_ATOMIC64_INIT(0),
-};
 static ihk_spinlock_t tod_data_lock = SPIN_LOCK_UNLOCKED;
 
 void check_signal(unsigned long, void *, int);