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Commit df211c8a authored by Nathan Lynch's avatar Nathan Lynch Committed by Paul Mackerras
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[POWERPC] Remove spinlock from struct cpu_purr_data 



cpu_purr_data is a per-cpu array used to account for stolen time on
partitioned systems.  It used to be the case that cpus accessed each
others' cpu_purr_data, so each entry was protected by a spinlock.

However, the code was reworked ("Simplify stolen time calculation")
with the result that each cpu accesses its own cpu_purr_data and not
those of other cpus.  This means we can get rid of the spinlock as
long as we're careful to disable interrupts when accessing
cpu_purr_data in process context.

Signed-off-by: default avatarNathan Lynch <ntl@pobox.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 1a06e0fe

arch/powerpc/kernel/time.c

+15 −9
Original line number Diff line number Diff line
@@ -222,19 +222,28 @@ struct cpu_purr_data { 
	int	initialized;			/* thread is running */

	u64	tb;			/* last TB value read */

	u64	purr;			/* last PURR value read */

	spinlock_t lock;

};



/*

 * Each entry in the cpu_purr_data array is manipulated only by its

 * "owner" cpu -- usually in the timer interrupt but also occasionally

 * in process context for cpu online.  As long as cpus do not touch

 * each others' cpu_purr_data, disabling local interrupts is

 * sufficient to serialize accesses.

 */

static DEFINE_PER_CPU(struct cpu_purr_data, cpu_purr_data);



static void snapshot_tb_and_purr(void *data)

{

	unsigned long flags;

	struct cpu_purr_data *p = &__get_cpu_var(cpu_purr_data);



	local_irq_save(flags);

	p->tb = mftb();

	p->purr = mfspr(SPRN_PURR);

	wmb();

	p->initialized = 1;

	local_irq_restore(flags);

}



/*
@@ -242,15 +251,14 @@ static void snapshot_tb_and_purr(void *data) 
 */

void snapshot_timebases(void)

{

	int cpu;



	if (!cpu_has_feature(CPU_FTR_PURR))

		return;

	for_each_possible_cpu(cpu)

		spin_lock_init(&per_cpu(cpu_purr_data, cpu).lock);

	on_each_cpu(snapshot_tb_and_purr, NULL, 0, 1);

}



/*

 * Must be called with interrupts disabled.

 */

void calculate_steal_time(void)

{

	u64 tb, purr;
@@ -262,7 +270,6 @@ void calculate_steal_time(void) 
	pme = &per_cpu(cpu_purr_data, smp_processor_id());

	if (!pme->initialized)

		return;		/* this can happen in early boot */

	spin_lock(&pme->lock);

	tb = mftb();

	purr = mfspr(SPRN_PURR);

	stolen = (tb - pme->tb) - (purr - pme->purr);
@@ -270,7 +277,6 @@ void calculate_steal_time(void) 
		account_steal_time(current, stolen);

	pme->tb = tb;

	pme->purr = purr;

	spin_unlock(&pme->lock);

}



/*
@@ -284,12 +290,12 @@ static void snapshot_purr(void) 


	if (!cpu_has_feature(CPU_FTR_PURR))

		return;

	local_irq_save(flags);

	pme = &per_cpu(cpu_purr_data, smp_processor_id());

	spin_lock_irqsave(&pme->lock, flags);

	pme->tb = mftb();

	pme->purr = mfspr(SPRN_PURR);

	pme->initialized = 1;

	spin_unlock_irqrestore(&pme->lock, flags);

	local_irq_restore(flags);

}



#endif /* CONFIG_PPC_SPLPAR */