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>

3 files changed, 13 insertions, 18 deletions

diff --git a/kernel/acct.c b/kernel/acct.c
index 1be013c6053e..a1844f14c6d6 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -458,9 +458,7 @@ static void do_acct_process(struct bsd_acct_struct *acct,
         acct_t ac;
         mm_segment_t fs;
         unsigned long flim;
-        u64 elapsed;
-        u64 run_time;
-        struct timespec uptime;
+        u64 elapsed, run_time;
         struct tty_struct *tty;
         const struct cred *orig_cred;
 
@@ -484,10 +482,8 @@ static void do_acct_process(struct bsd_acct_struct *acct,
         strlcpy(ac.ac_comm, current->comm, sizeof(ac.ac_comm));
 
         /* calculate run_time in nsec*/
-        ktime_get_ts(&uptime);
-        run_time = (u64)uptime.tv_sec*NSEC_PER_SEC + uptime.tv_nsec;
-        run_time -= (u64)current->group_leader->start_time.tv_sec * NSEC_PER_SEC
-                       + current->group_leader->start_time.tv_nsec;
+        run_time = ktime_get_ns();
+        run_time -= current->group_leader->start_time;
         /* convert nsec -> AHZ */
         elapsed = nsec_to_AHZ(run_time);
 #if ACCT_VERSION==3
diff --git a/kernel/fork.c b/kernel/fork.c
index a7ab82db2f60..627b7f80afb0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1262,7 +1262,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 
         posix_cpu_timers_init(p);
 
-        ktime_get_ts(&p->start_time);
+        p->start_time = ktime_get_ns();
         p->real_start_time = ktime_get_boot_ns();
         p->io_context = NULL;
         p->audit_context = NULL;
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)