sched: make use of precise accounting for /proc task stats

make use of CFS's precise accounting to drive /proc/<pid>/stat statistics.

this code was co-authored by:

 Balbir Singh <balbir@linux.vnet.ibm.com>
 Dmitry Adamushko <dmitry.adamushko@gmail.com>
 Ingo Molnar <mingo@elte.hu>

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>

1 files changed, 47 insertions, 10 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 3df644313f9b..98e78e2f18d6 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -310,6 +310,41 @@ int proc_pid_status(struct task_struct *task, char * buffer)
         return buffer - orig;
 }
 
+static clock_t task_utime(struct task_struct *p)
+{
+        clock_t utime = cputime_to_clock_t(p->utime),
+                total = utime + cputime_to_clock_t(p->stime);
+        u64 temp;
+
+        /*
+         * Use CFS's precise accounting:
+         */
+        temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
+
+        if (total) {
+                temp *= utime;
+                do_div(temp, total);
+        }
+        utime = (clock_t)temp;
+
+        return utime;
+}
+
+static clock_t task_stime(struct task_struct *p)
+{
+        clock_t stime = cputime_to_clock_t(p->stime);
+
+        /*
+         * Use CFS's precise accounting. (we subtract utime from
+         * the total, to make sure the total observed by userspace
+         * grows monotonically - apps rely on that):
+         */
+        stime = nsec_to_clock_t(p->se.sum_exec_runtime) - task_utime(p);
+
+        return stime;
+}
+
+
 static int do_task_stat(struct task_struct *task, char * buffer, int whole)
 {
         unsigned long vsize, eip, esp, wchan = ~0UL;
@@ -324,7 +359,8 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
         unsigned long long start_time;
         unsigned long cmin_flt = 0, cmaj_flt = 0;
         unsigned long  min_flt = 0,  maj_flt = 0;
-        cputime_t cutime, cstime, utime, stime;
+        cputime_t cutime, cstime;
+        clock_t utime, stime;
         unsigned long rsslim = 0;
         char tcomm[sizeof(task->comm)];
         unsigned long flags;
@@ -342,7 +378,8 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
 
         sigemptyset(&sigign);
         sigemptyset(&sigcatch);
-        cutime = cstime = utime = stime = cputime_zero;
+        cutime = cstime = cputime_zero;
+        utime = stime = 0;
 
         rcu_read_lock();
         if (lock_task_sighand(task, &flags)) {
@@ -368,15 +405,15 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
                         do {
                                 min_flt += t->min_flt;
                                 maj_flt += t->maj_flt;
-                                utime = cputime_add(utime, t->utime);
-                                stime = cputime_add(stime, t->stime);
+                                utime += task_utime(t);
+                                stime += task_stime(t);
                                 t = next_thread(t);
                         } while (t != task);
 
                         min_flt += sig->min_flt;
                         maj_flt += sig->maj_flt;
-                        utime = cputime_add(utime, sig->utime);
-                        stime = cputime_add(stime, sig->stime);
+                        utime += cputime_to_clock_t(sig->utime);
+                        stime += cputime_to_clock_t(sig->stime);
                 }
 
                 sid = signal_session(sig);
@@ -392,8 +429,8 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
         if (!whole) {
                 min_flt = task->min_flt;
                 maj_flt = task->maj_flt;
-                utime = task->utime;
-                stime = task->stime;
+                utime = task_utime(task);
+                stime = task_stime(task);
         }
 
         /* scale priority and nice values from timeslices to -20..20 */
@@ -424,8 +461,8 @@ static int do_task_stat(struct task_struct *task, char * buffer, int whole)
                 cmin_flt,
                 maj_flt,
                 cmaj_flt,
-                cputime_to_clock_t(utime),
-                cputime_to_clock_t(stime),
+                utime,
+                stime,
                 cputime_to_clock_t(cutime),
                 cputime_to_clock_t(cstime),
                 priority,