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s390/vtime: correct system time accounting 

There is a slight misaccounting of system time in vtime_account_user.
This function is called once per HZ tick in interrupt context.
The irq_enter function already accounted the system time up to the
point of the irq_enter call. The system time from irq_enter until
vtime_account_user/do_account_vtime is reached is irq time but it
is accounted to the previous context.

Just drop the hardirq offset from arch/s390/kernel/vtime.c.

Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2016-12-20 07:27:59 +01:00
parent e93b1cc8a8
commit 8f2b468aad
1 changed files with 4 additions and 4 deletions
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8
arch/s390/kernel/vtime.c
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@ -94,7 +94,7 @@ static void update_mt_scaling(void)
* Update process times based on virtual cpu times stored by entry.S
* to the lowcore fields user_timer, system_timer & steal_clock.
*/
static int do_account_vtime(struct task_struct *tsk, int hardirq_offset)
static int do_account_vtime(struct task_struct *tsk)
{
u64 timer, clock, user, system, steal;
u64 user_scaled, system_scaled;
@ -138,7 +138,7 @@ static int do_account_vtime(struct task_struct *tsk, int hardirq_offset)
}
account_user_time(tsk, user);
tsk->utimescaled += user_scaled;
account_system_time(tsk, hardirq_offset, system);
account_system_time(tsk, 0, system);
tsk->stimescaled += system_scaled;
steal = S390_lowcore.steal_timer;
@ -152,7 +152,7 @@ static int do_account_vtime(struct task_struct *tsk, int hardirq_offset)
void vtime_task_switch(struct task_struct *prev)
{
do_account_vtime(prev, 0);
do_account_vtime(prev);
prev->thread.user_timer = S390_lowcore.user_timer;
prev->thread.system_timer = S390_lowcore.system_timer;
S390_lowcore.user_timer = current->thread.user_timer;
@ -166,7 +166,7 @@ void vtime_task_switch(struct task_struct *prev)
*/
void vtime_account_user(struct task_struct *tsk)
{
if (do_account_vtime(tsk, HARDIRQ_OFFSET))
if (do_account_vtime(tsk))
virt_timer_expire();
}