sched: Make task->start_time nanoseconds based

Simplify the timespec to nsec/usec conversions.

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

1 files changed, 9 insertions, 10 deletions

diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index ea6d170452c4..975cb49e32bf 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -31,20 +31,19 @@ void bacct_add_tsk(struct user_namespace *user_ns,
                    struct taskstats *stats, struct task_struct *tsk)
 {
         const struct cred *tcred;
-        struct timespec uptime, ts;
         cputime_t utime, stime, utimescaled, stimescaled;
-        u64 ac_etime;
+        u64 delta;
 
         BUILD_BUG_ON(TS_COMM_LEN < TASK_COMM_LEN);
 
-        /* calculate task elapsed time in timespec */
-        ktime_get_ts(&uptime);
-        ts = timespec_sub(uptime, tsk->start_time);
-        /* rebase elapsed time to usec (should never be negative) */
-        ac_etime = timespec_to_ns(&ts);
-        do_div(ac_etime, NSEC_PER_USEC);
-        stats->ac_etime = ac_etime;
-        stats->ac_btime = get_seconds() - ts.tv_sec;
+        /* calculate task elapsed time in nsec */
+        delta = ktime_get_ns() - tsk->start_time;
+        /* Convert to micro seconds */
+        do_div(delta, NSEC_PER_USEC);
+        stats->ac_etime = delta;
+        /* Convert to seconds for btime */
+        do_div(delta, USEC_PER_SEC);
+        stats->ac_btime = get_seconds() - delta;
         if (thread_group_leader(tsk)) {
                 stats->ac_exitcode = tsk->exit_code;
                 if (tsk->flags & PF_FORKNOEXEC)