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>

3 files changed, 3 insertions, 9 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 64db2bceac59..d7f9199217bb 100644
--- a/fs/proc/array.c
+++ b/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);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 306f4f0c987a..67678fa76f99 100644
--- a/include/linux/sched.h
+++ b/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;
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 8f541930ce26..a7ab82db2f60 100644
--- a/kernel/fork.c
+++ b/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)