* Peter Zijlstra <[email protected]> wrote:
> > + prev_cpu = smp_processor_id();
> > rep_nop();
> > + preempt_enable();
>
> Why not have the rep_nop() here between the enable, and disable ?
yes, indeed - fixed.
> > + /*
> > + * If we preempted we skip this small amount of time:
> ^ migrated, perhaps?
yeah, fixed.
updated patch below.
Ingo
---------------->
Subject: x86: make delay_tsc() preemptible again
From: Ingo Molnar <[email protected]>
make delay_tsc() preemptible again.
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
---
arch/x86/lib/delay_32.c | 27 ++++++++++++++++++++++-----
arch/x86/lib/delay_64.c | 29 +++++++++++++++++++++++------
2 files changed, 45 insertions(+), 11 deletions(-)
Index: linux/arch/x86/lib/delay_32.c
===================================================================
--- linux.orig/arch/x86/lib/delay_32.c
+++ linux/arch/x86/lib/delay_32.c
@@ -38,17 +38,34 @@ static void delay_loop(unsigned long loo
:"0" (loops));
}
-/* TSC based delay: */
+/*
+ * TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
static void delay_tsc(unsigned long loops)
{
- unsigned long bclock, now;
+ unsigned long prev, now;
+ long left = loops;
+ int prev_cpu, cpu;
- preempt_disable(); /* TSC's are per-cpu */
- rdtscl(bclock);
+ preempt_disable();
+ rdtscl(prev);
do {
+ prev_cpu = smp_processor_id();
+ preempt_enable();
rep_nop();
+ preempt_disable();
+ cpu = smp_processor_id();
rdtscl(now);
- } while ((now-bclock) < loops);
+ /*
+ * If we migrated we skip this small amount of time:
+ */
+ if (prev_cpu != cpu)
+ prev = now;
+ left -= now - prev;
+ prev = now;
+ } while (left > 0);
preempt_enable();
}
Index: linux/arch/x86/lib/delay_64.c
===================================================================
--- linux.orig/arch/x86/lib/delay_64.c
+++ linux/arch/x86/lib/delay_64.c
@@ -26,17 +26,34 @@ int read_current_timer(unsigned long *ti
return 0;
}
+/*
+ * TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
void __delay(unsigned long loops)
{
- unsigned bclock, now;
+ unsigned long prev, now;
+ long left = loops;
+ int prev_cpu, cpu;
- preempt_disable(); /* TSC's are pre-cpu */
- rdtscl(bclock);
+ preempt_disable();
+ rdtscl(prev);
do {
- rep_nop();
+ prev_cpu = smp_processor_id();
+ preempt_enable();
+ rep_nop();
+ preempt_disable();
+ cpu = smp_processor_id();
rdtscl(now);
- }
- while ((now-bclock) < loops);
+ /*
+ * If we migrated we skip this small amount of time:
+ */
+ if (prev_cpu != cpu)
+ prev = now;
+ left -= now - prev;
+ prev = now;
+ } while (left > 0);
preempt_enable();
}
EXPORT_SYMBOL(__delay);
-
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