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Diffstat (limited to 'arch/x86/lib/delay_64.c')
-rw-r--r--arch/x86/lib/delay_64.c30
1 files changed, 26 insertions, 4 deletions
diff --git a/arch/x86/lib/delay_64.c b/arch/x86/lib/delay_64.c
index bbc61051851..4c441be9264 100644
--- a/arch/x86/lib/delay_64.c
+++ b/arch/x86/lib/delay_64.c
@@ -31,14 +31,36 @@ int __devinit read_current_timer(unsigned long *timer_value)
void __delay(unsigned long loops)
{
unsigned bclock, now;
+ int cpu;
- preempt_disable(); /* TSC's are pre-cpu */
+ preempt_disable();
+ cpu = smp_processor_id();
rdtscl(bclock);
- do {
- rep_nop();
+ for (;;) {
rdtscl(now);
+ if ((now - bclock) >= loops)
+ break;
+
+ /* Allow RT tasks to run */
+ preempt_enable();
+ rep_nop();
+ preempt_disable();
+
+ /*
+ * It is possible that we moved to another CPU, and
+ * since TSC's are per-cpu we need to calculate
+ * that. The delay must guarantee that we wait "at
+ * least" the amount of time. Being moved to another
+ * CPU could make the wait longer but we just need to
+ * make sure we waited long enough. Rebalance the
+ * counter for this CPU.
+ */
+ if (unlikely(cpu != smp_processor_id())) {
+ loops -= (now - bclock);
+ cpu = smp_processor_id();
+ rdtscl(bclock);
+ }
}
- while ((now-bclock) < loops);
preempt_enable();
}
EXPORT_SYMBOL(__delay);