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Commit fe44d621 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Fix the irqtime code to deal with u64 wraps 



Some ARM systems have a short sched_clock() [ which needs to be fixed
too ], but this exposed a bug in the irq_time code as well, it doesn't
deal with wraps at all.

Fix the irq_time code to deal with u64 wraps by re-writing the code to
only use delta increments, which avoids the whole issue.

Reviewed-by: default avatarVenkatesh Pallipadi <venki@google.com>
Reported-by: default avatarMikael Pettersson <mikpe@it.uu.se>
Tested-by: default avatarMikael Pettersson <mikpe@it.uu.se>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1292242433.6803.199.camel@twins>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent dbd87b5a

kernel/sched.c

+50 −33
Original line number Original line Diff line number Diff line
@@ -636,23 +636,18 @@ static inline struct task_group *task_group(struct task_struct *p) 




#endif /* CONFIG_CGROUP_SCHED */

#endif /* CONFIG_CGROUP_SCHED */





static u64 irq_time_cpu(int cpu);

static void update_rq_clock_task(struct rq *rq, s64 delta);

static void sched_irq_time_avg_update(struct rq *rq, u64 irq_time);





inline void update_rq_clock(struct rq *rq)

static void update_rq_clock(struct rq *rq)

{

{

	int cpu = cpu_of(rq);

	s64 delta;

	u64 irq_time;





	if (rq->skip_clock_update)

	if (rq->skip_clock_update)

		return;

		return;





	rq->clock = sched_clock_cpu(cpu);

	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;

	irq_time = irq_time_cpu(cpu);

	rq->clock += delta;

	if (rq->clock - irq_time > rq->clock_task)

	update_rq_clock_task(rq, delta);

		rq->clock_task = rq->clock - irq_time;



	sched_irq_time_avg_update(rq, irq_time);

}

}





/*

/*
@@ -1946,19 +1941,20 @@ void disable_sched_clock_irqtime(void) 
	sched_clock_irqtime = 0;

	sched_clock_irqtime = 0;

}

}





static u64 irq_time_cpu(int cpu)

static inline u64 irq_time_cpu(int cpu)

{

{

	if (!sched_clock_irqtime)

		return 0;



	return per_cpu(cpu_softirq_time, cpu) + per_cpu(cpu_hardirq_time, cpu);

	return per_cpu(cpu_softirq_time, cpu) + per_cpu(cpu_hardirq_time, cpu);

}

}





/*

 * Called before incrementing preempt_count on {soft,}irq_enter

 * and before decrementing preempt_count on {soft,}irq_exit.

 */

void account_system_vtime(struct task_struct *curr)

void account_system_vtime(struct task_struct *curr)

{

{

	unsigned long flags;

	unsigned long flags;

	s64 delta;

	int cpu;

	int cpu;

	u64 now, delta;





	if (!sched_clock_irqtime)

	if (!sched_clock_irqtime)

		return;

		return;
@@ -1966,9 +1962,9 @@ void account_system_vtime(struct task_struct *curr) 
	local_irq_save(flags);

	local_irq_save(flags);





	cpu = smp_processor_id();

	cpu = smp_processor_id();

	now = sched_clock_cpu(cpu);

	delta = sched_clock_cpu(cpu) - __this_cpu_read(irq_start_time);

	delta = now - per_cpu(irq_start_time, cpu);

	__this_cpu_add(irq_start_time, delta);

	per_cpu(irq_start_time, cpu) = now;



	/*

	/*

	 * We do not account for softirq time from ksoftirqd here.

	 * We do not account for softirq time from ksoftirqd here.

	 * We want to continue accounting softirq time to ksoftirqd thread

	 * We want to continue accounting softirq time to ksoftirqd thread
@@ -1976,33 +1972,54 @@ void account_system_vtime(struct task_struct *curr) 
	 * that do not consume any time, but still wants to run.

	 * that do not consume any time, but still wants to run.

	 */

	 */

	if (hardirq_count())

	if (hardirq_count())

		per_cpu(cpu_hardirq_time, cpu) += delta;

		__this_cpu_add(cpu_hardirq_time, delta);

	else if (in_serving_softirq() && !(curr->flags & PF_KSOFTIRQD))

	else if (in_serving_softirq() && !(curr->flags & PF_KSOFTIRQD))

		per_cpu(cpu_softirq_time, cpu) += delta;

		__this_cpu_add(cpu_softirq_time, delta);





	local_irq_restore(flags);

	local_irq_restore(flags);

}

}

EXPORT_SYMBOL_GPL(account_system_vtime);

EXPORT_SYMBOL_GPL(account_system_vtime);





static void sched_irq_time_avg_update(struct rq *rq, u64 curr_irq_time)

static void update_rq_clock_task(struct rq *rq, s64 delta)

{

{

	if (sched_clock_irqtime && sched_feat(NONIRQ_POWER)) {

	s64 irq_delta;

		u64 delta_irq = curr_irq_time - rq->prev_irq_time;



		rq->prev_irq_time = curr_irq_time;

	irq_delta = irq_time_cpu(cpu_of(rq)) - rq->prev_irq_time;

		sched_rt_avg_update(rq, delta_irq);



	}

	/*

	 * Since irq_time is only updated on {soft,}irq_exit, we might run into

	 * this case when a previous update_rq_clock() happened inside a

	 * {soft,}irq region.

	 *

	 * When this happens, we stop ->clock_task and only update the

	 * prev_irq_time stamp to account for the part that fit, so that a next

	 * update will consume the rest. This ensures ->clock_task is

	 * monotonic.

	 *

	 * It does however cause some slight miss-attribution of {soft,}irq

	 * time, a more accurate solution would be to update the irq_time using

	 * the current rq->clock timestamp, except that would require using

	 * atomic ops.

	 */

	if (irq_delta > delta)

		irq_delta = delta;



	rq->prev_irq_time += irq_delta;

	delta -= irq_delta;

	rq->clock_task += delta;



	if (irq_delta && sched_feat(NONIRQ_POWER))

		sched_rt_avg_update(rq, irq_delta);

}

}





#else

#else /* CONFIG_IRQ_TIME_ACCOUNTING */





static u64 irq_time_cpu(int cpu)

static void update_rq_clock_task(struct rq *rq, s64 delta)

{

{

	return 0;

	rq->clock_task += delta;

}

}





static void sched_irq_time_avg_update(struct rq *rq, u64 curr_irq_time) { }

#endif /* CONFIG_IRQ_TIME_ACCOUNTING */



#endif





#include "sched_idletask.c"

#include "sched_idletask.c"

#include "sched_fair.c"

#include "sched_fair.c"