Commit 8f2b468a authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent e93b1cc8

arch/s390/kernel/vtime.c

+4 −4
Original line number Diff line number Diff line
@@ -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();

}

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