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[POWERPC] Remove spinlock from struct cpu_purr_data

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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: Nathan Lynch <ntl@pobox.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
Nathan Lynch 2007-05-23 10:51:25 +10:00 committed by Paul Mackerras
parent 1a06e0fe96
commit df211c8a47
1 changed files with 15 additions and 9 deletions
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24
arch/powerpc/kernel/time.c
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@ -222,19 +222,28 @@ struct cpu_purr_data {
int initialized; /* thread is running */ int initialized; /* thread is running */
u64 tb; /* last TB value read */ u64 tb; /* last TB value read */
u64 purr; /* last PURR 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 DEFINE_PER_CPU(struct cpu_purr_data, cpu_purr_data);
static void snapshot_tb_and_purr(void *data) static void snapshot_tb_and_purr(void *data)
{ {
unsigned long flags;
struct cpu_purr_data *p = &__get_cpu_var(cpu_purr_data); struct cpu_purr_data *p = &__get_cpu_var(cpu_purr_data);
local_irq_save(flags);
p->tb = mftb(); p->tb = mftb();
p->purr = mfspr(SPRN_PURR); p->purr = mfspr(SPRN_PURR);
wmb(); wmb();
p->initialized = 1; p->initialized = 1;
local_irq_restore(flags);
} }
/* /*
@ -242,15 +251,14 @@ static void snapshot_tb_and_purr(void *data)
*/ */
void snapshot_timebases(void) void snapshot_timebases(void)
{ {
int cpu;
if (!cpu_has_feature(CPU_FTR_PURR)) if (!cpu_has_feature(CPU_FTR_PURR))
return; 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); on_each_cpu(snapshot_tb_and_purr, NULL, 0, 1);
} }
/*
* Must be called with interrupts disabled.
*/
void calculate_steal_time(void) void calculate_steal_time(void)
{ {
u64 tb, purr; u64 tb, purr;
@ -262,7 +270,6 @@ void calculate_steal_time(void)
pme = &per_cpu(cpu_purr_data, smp_processor_id()); pme = &per_cpu(cpu_purr_data, smp_processor_id());
if (!pme->initialized) if (!pme->initialized)
return; /* this can happen in early boot */ return; /* this can happen in early boot */
spin_lock(&pme->lock);
tb = mftb(); tb = mftb();
purr = mfspr(SPRN_PURR); purr = mfspr(SPRN_PURR);
stolen = (tb - pme->tb) - (purr - pme->purr); stolen = (tb - pme->tb) - (purr - pme->purr);
@ -270,7 +277,6 @@ void calculate_steal_time(void)
account_steal_time(current, stolen); account_steal_time(current, stolen);
pme->tb = tb; pme->tb = tb;
pme->purr = purr; pme->purr = purr;
spin_unlock(&pme->lock);
} }
/* /*
@ -284,12 +290,12 @@ static void snapshot_purr(void)
if (!cpu_has_feature(CPU_FTR_PURR)) if (!cpu_has_feature(CPU_FTR_PURR))
return; return;
local_irq_save(flags);
pme = &per_cpu(cpu_purr_data, smp_processor_id()); pme = &per_cpu(cpu_purr_data, smp_processor_id());
spin_lock_irqsave(&pme->lock, flags);
pme->tb = mftb(); pme->tb = mftb();
pme->purr = mfspr(SPRN_PURR); pme->purr = mfspr(SPRN_PURR);
pme->initialized = 1; pme->initialized = 1;
spin_unlock_irqrestore(&pme->lock, flags); local_irq_restore(flags);
} }
#endif /* CONFIG_PPC_SPLPAR */ #endif /* CONFIG_PPC_SPLPAR */