sched/cputime: Fix cpu_timer_sample_group() double accounting

While looking over the cpu-timer code I found that we appear to add
the delta for the calling task twice, through:

  cpu_timer_sample_group()
    thread_group_cputimer()
      thread_group_cputime()
        times->sum_exec_runtime += task_sched_runtime();

    *sample = cputime.sum_exec_runtime + task_delta_exec();

Which would make the sample run ahead, making the sleep short.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/20141112113737.GI10476@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 1 insertions, 14 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5f12ca65c9a7..797a6c84c48d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2499,19 +2499,6 @@ static u64 do_task_delta_exec(struct task_struct *p, struct rq *rq)
         return ns;
 }
 
-unsigned long long task_delta_exec(struct task_struct *p)
-{
-        unsigned long flags;
-        struct rq *rq;
-        u64 ns = 0;
-
-        rq = task_rq_lock(p, &flags);
-        ns = do_task_delta_exec(p, rq);
-        task_rq_unlock(rq, p, &flags);
-
-        return ns;
-}
-
 /*
  * Return accounted runtime for the task.
  * In case the task is currently running, return the runtime plus current's
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 492b986195d5..a16b67859e2a 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -553,7 +553,7 @@ static int cpu_timer_sample_group(const clockid_t which_clock,
                 *sample = cputime_to_expires(cputime.utime);
                 break;
         case CPUCLOCK_SCHED:
-                *sample = cputime.sum_exec_runtime + task_delta_exec(p);
+                *sample = cputime.sum_exec_runtime;
                 break;
         }
         return 0;