commit 4cd4c1b40d40447fb5e7ba80746c6d7ba91d7a53
author Peter Zijlstra <a.p.zijlstra@chello.nl> Thu Feb 05 12:24:16 2009 +0100
committer Ingo Molnar <mingo@elte.hu> Thu Feb 05 13:04:33 2009 +0100
tree b1e580d5284648d6884e951d995509094a92cca4
parent 32bd671d6cbeda60dc73be77fa2b9037d9a9bfa0

timers: split process wide cpu clocks/timers

Change the process wide cpu timers/clocks so that we:

 1) don't mess up the kernel with too many threads,
 2) don't have a per-cpu allocation for each process,
 3) have no impact when not used.

In order to accomplish this we're going to split it into two parts:

 - clocks; which can take all the time they want since they run
           from user context -- ie. sys_clock_gettime(CLOCK_PROCESS_CPUTIME_ID)

 - timers; which need constant time sampling but since they're
           explicity used, the user can pay the overhead.

The clock readout will go back to a full sum of the thread group, while the
timers will run of a global 'clock' that only runs when needed, so only
programs that make use of the facility pay the price.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_stats.h

diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 8ab0cef..a8f93dd 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -296,19 +296,21 @@
 static inline void account_group_user_time(struct task_struct *tsk,
 					   cputime_t cputime)
 {
-	struct task_cputime *times;
-	struct signal_struct *sig;
+	struct thread_group_cputimer *cputimer;
 
 	/* tsk == current, ensure it is safe to use ->signal */
 	if (unlikely(tsk->exit_state))
 		return;
 
-	sig = tsk->signal;
-	times = &sig->cputime.totals;
+	cputimer = &tsk->signal->cputimer;
 
-	spin_lock(&times->lock);
-	times->utime = cputime_add(times->utime, cputime);
-	spin_unlock(&times->lock);
+	if (!cputimer->running)
+		return;
+
+	spin_lock(&cputimer->lock);
+	cputimer->cputime.utime =
+		cputime_add(cputimer->cputime.utime, cputime);
+	spin_unlock(&cputimer->lock);
 }
 
 /**
@@ -324,19 +326,21 @@
 static inline void account_group_system_time(struct task_struct *tsk,
 					     cputime_t cputime)
 {
-	struct task_cputime *times;
-	struct signal_struct *sig;
+	struct thread_group_cputimer *cputimer;
 
 	/* tsk == current, ensure it is safe to use ->signal */
 	if (unlikely(tsk->exit_state))
 		return;
 
-	sig = tsk->signal;
-	times = &sig->cputime.totals;
+	cputimer = &tsk->signal->cputimer;
 
-	spin_lock(&times->lock);
-	times->stime = cputime_add(times->stime, cputime);
-	spin_unlock(&times->lock);
+	if (!cputimer->running)
+		return;
+
+	spin_lock(&cputimer->lock);
+	cputimer->cputime.stime =
+		cputime_add(cputimer->cputime.stime, cputime);
+	spin_unlock(&cputimer->lock);
 }
 
 /**
@@ -352,7 +356,7 @@
 static inline void account_group_exec_runtime(struct task_struct *tsk,
 					      unsigned long long ns)
 {
-	struct task_cputime *times;
+	struct thread_group_cputimer *cputimer;
 	struct signal_struct *sig;
 
 	sig = tsk->signal;
@@ -361,9 +365,12 @@
 	if (unlikely(!sig))
 		return;
 
-	times = &sig->cputime.totals;
+	cputimer = &sig->cputimer;
 
-	spin_lock(&times->lock);
-	times->sum_exec_runtime += ns;
-	spin_unlock(&times->lock);
+	if (!cputimer->running)
+		return;
+
+	spin_lock(&cputimer->lock);
+	cputimer->cputime.sum_exec_runtime += ns;
+	spin_unlock(&cputimer->lock);
 }