sched: restore deterministic CPU accounting on powerpc

Since powerpc started using CONFIG_GENERIC_CLOCKEVENTS, the
deterministic CPU accounting (CONFIG_VIRT_CPU_ACCOUNTING) has been
broken on powerpc, because we end up counting user time twice: once in
timer_interrupt() and once in update_process_times().

This fixes the problem by pulling the code in update_process_times
that updates utime and stime into a separate function called
account_process_tick.  If CONFIG_VIRT_CPU_ACCOUNTING is not defined,
there is a version of account_process_tick in kernel/timer.c that
simply accounts a whole tick to either utime or stime as before.  If
CONFIG_VIRT_CPU_ACCOUNTING is defined, then arch code gets to
implement account_process_tick.

This also lets us simplify the s390 code a bit; it means that the s390
timer interrupt can now call update_process_times even when
CONFIG_VIRT_CPU_ACCOUNTING is turned on, and can just implement a
suitable account_process_tick().

account_process_tick() now takes the task_struct * as an argument.
Tested both with and without CONFIG_VIRT_CPU_ACCOUNTING.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 14 insertions, 7 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index 00e44e2..a05817c 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -817,6 +817,19 @@ unsigned long next_timer_interrupt(void)
 
 #endif
 
+#ifndef CONFIG_VIRT_CPU_ACCOUNTING
+void account_process_tick(struct task_struct *p, int user_tick)
+{
+	if (user_tick) {
+		account_user_time(p, jiffies_to_cputime(1));
+		account_user_time_scaled(p, jiffies_to_cputime(1));
+	} else {
+		account_system_time(p, HARDIRQ_OFFSET, jiffies_to_cputime(1));
+		account_system_time_scaled(p, jiffies_to_cputime(1));
+	}
+}
+#endif
+
 /*
  * Called from the timer interrupt handler to charge one tick to the current
  * process.  user_tick is 1 if the tick is user time, 0 for system.
@@ -827,13 +840,7 @@ void update_process_times(int user_tick)
 	int cpu = smp_processor_id();
 
 	/* Note: this timer irq context must be accounted for as well. */
-	if (user_tick) {
-		account_user_time(p, jiffies_to_cputime(1));
-		account_user_time_scaled(p, jiffies_to_cputime(1));
-	} else {
-		account_system_time(p, HARDIRQ_OFFSET, jiffies_to_cputime(1));
-		account_system_time_scaled(p, jiffies_to_cputime(1));
-	}
+	account_process_tick(p, user_tick);
 	run_local_timers();
 	if (rcu_pending(cpu))
 		rcu_check_callbacks(cpu, user_tick);