On Wed, 3 Dec 2014, Linus Torvalds wrote:
> On Wed, Dec 3, 2014 at 12:55 PM, Thomas Gleixner <t...@linutronix.de> wrote:
> >
> > But it's always negative, which means HPET is always ahead of
> > TSC. That excludes pretty much the clocksource watchdog starvation
> > issue which results in TSC being ahead of HPET due to a HPET
> > wraparound (which takes ~300s).
>
> Still, I'd be more likely to trust the TSC than the HPET on modern
> machines.. And DaveJ's machine isn't some old one.
Well, that does not explain the softlock watchdog which is solely
relying on the TSC.
> Of course, there's always BIOS games. Can we read the TSC offset
> register and check it being constant (modulo sleep events)?
The kernel does not touch it. Here is a untested hack to verify it on
every local apic timer interrupt. Not nice, but simple :)
Thanks.
tglx
---
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index ba6cc041edb1..69b0a8143e83 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -554,6 +554,7 @@ static struct clock_event_device lapic_clockevent = {
.irq = -1,
};
static DEFINE_PER_CPU(struct clock_event_device, lapic_events);
+static DEFINE_PER_CPU(u64, tsc_adjust);
/*
* Setup the local APIC timer for this CPU. Copy the initialized values
@@ -569,6 +570,13 @@ static void setup_APIC_timer(void)
lapic_clockevent.rating = 150;
}
+ if (this_cpu_has(X86_FEATURE_TSC_ADJUST)) {
+ u64 adj;
+
+ rdmsrl(MSR_IA32_TSC_ADJUST, adj);
+ __this_cpu_write(tsc_adjust, adj);
+ }
+
memcpy(levt, &lapic_clockevent, sizeof(*levt));
levt->cpumask = cpumask_of(smp_processor_id());
@@ -912,6 +920,19 @@ static void local_apic_timer_interrupt(void)
return;
}
+ if (this_cpu_has(X86_FEATURE_TSC_ADJUST)) {
+ u64 adj;
+
+ rdmsrl(MSR_IA32_TSC_ADJUST, adj);
+ if (adj != __this_cpu_read(tsc_adjust)) {
+ pr_err("TSC adjustment on cpu %d changed %llu ->
%llu\n",
+ cpu,
+ (unsigned long long) __this_cpu_read(tsc_adjust),
+ (unsigned long long) adj);
+ __this_cpu_write(tsc_adjust, adj);
+ }
+ }
+
/*
* the NMI deadlock-detector uses this.
*/
--
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