sched: Make task->real_start_time nanoseconds based

Simplify the only user of this data by removing the timespec
conversion.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

fs/proc/array.c

@@ -473,13 +473,8 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 	priority = task_prio(task);
 	nice = task_nice(task);
 
-	/* Temporary variable needed for gcc-2.96 */
-	/* convert timespec -> nsec*/
-	start_time =
-		(unsigned long long)task->real_start_time.tv_sec * NSEC_PER_SEC
-				+ task->real_start_time.tv_nsec;
 	/* convert nsec -> ticks */
-	start_time = nsec_to_clock_t(start_time);
+	start_time = nsec_to_clock_t(task->real_start_time);
 
 	seq_printf(m, "%d (%s) %c", pid_nr_ns(pid, ns), tcomm, state);
 	seq_put_decimal_ll(m, ' ', ppid);

include/linux/sched.h

@@ -1368,7 +1368,7 @@ struct task_struct {
 #endif
 	unsigned long nvcsw, nivcsw; /* context switch counts */
 	struct timespec start_time; 		/* monotonic time */
-	struct timespec real_start_time;	/* boot based time */
+	u64 real_start_time;	/* boot based time in nsec */
 /* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
 	unsigned long min_flt, maj_flt;
 

kernel/fork.c

@@ -1263,8 +1263,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	posix_cpu_timers_init(p);
 
 	ktime_get_ts(&p->start_time);
-	p->real_start_time = p->start_time;
-	monotonic_to_bootbased(&p->real_start_time);
+	p->real_start_time = ktime_get_boot_ns();
 	p->io_context = NULL;
 	p->audit_context = NULL;
 	if (clone_flags & CLONE_THREAD)