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Subject[PATCH] timers: fix TIMER_ABSTIME for process wide cpu timers
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Date
While going through the man-pages Michael prepared for the posix timer
interface I realized that posix timers do expose the absolute time value
through the use of TIMER_ABSTIME.

---
Subject: timers: fix TIMER_ABSTIME for process wide cpu timers
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Wed Feb 11 11:30:27 CET 2009
The POSIX timer interface allows for absolute time expiry values through the
TIMER_ABSTIME flag, therefore we have to synchronize the timer to the clock
every time we start it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/sched.h | 13 +------------
kernel/posix-cpu-timers.c | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+), 12 deletions(-)
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -2229,18 +2229,7 @@ static inline int spin_needbreak(spinloc
* Thread group CPU time accounting.
*/
void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times);
-
-static inline
-void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
-{
- struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
- unsigned long flags;
-
- spin_lock_irqsave(&cputimer->lock, flags);
- cputimer->running = 1;
- *times = cputimer->cputime;
- spin_unlock_irqrestore(&cputimer->lock, flags);
-}
+void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times);

static inline void thread_group_cputime_init(struct signal_struct *sig)
{
Index: linux-2.6/kernel/posix-cpu-timers.c
===================================================================
--- linux-2.6.orig/kernel/posix-cpu-timers.c
+++ linux-2.6/kernel/posix-cpu-timers.c
@@ -261,6 +261,40 @@ out:
rcu_read_unlock();
}

+static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
+{
+ if (cputime_gt(b->utime, a->utime))
+ a->utime = b->utime;
+
+ if (cputime_gt(b->stime, a->stime))
+ a->stime = b->stime;
+
+ if (b->sum_exec_runtime > a->sum_exelt rec_runtime)
+ a->sum_exec_runtime = b->sum_exec_runtime;
+}
+
+void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
+{
+ struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+ struct task_cputime sum;
+ unsigned long flags;
+
+ spin_lock_irqsave(&cputimer->lock, flags);
+ if (!cputimer->running) {
+ cputimer->running = 1;
+ /*
+ * The POSIX timer interface allows for absolute time expiry
+ * values through the TIMER_ABSTIME flag, therefore we have
+ * to synchronize the timer to the clock every time we start
+ * it.
+ */
+ thread_group_cputime(tsk, &sum);
+ update_gt_cputime(&cputimer->cputime, &sum);
+ }
+ *times = cputimer->cputime;
+ spin_unlock_irqrestore(&cputimer->lock, flags);
+}
+
/*
* Sample a process (thread group) clock for the given group_leader task.
* Must be called with tasklist_lock held for reading.


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