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Subject[PATCH v4 2/2] arch, x86, tsc: inform TSC deadline clockevent device about recalibration
Date
The TSC deadline clockevent devices' configuration and registration
happens before the TSC frequency calibration is refined in
tsc_refine_calibration_work().

This results in the TSC clocksource and the TSC deadline clockevent
devices being configured with slightly different frequencies: the former
gets the refined one and the latter are configured with the inaccurate
frequency detected earlier by means of the
"Fast TSC calibration using PIT".

Within the APIC code, introduce the notifier function
lapic_update_tsc_freq() which reconfigures all per-CPU TSC deadline
clockevent devices with the current tsc_khz.

Call it from the TSC code after TSC calibration refinement has happened.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---
arch/x86/include/asm/apic.h | 1 +
arch/x86/kernel/apic/apic.c | 24 ++++++++++++++++++++++++
arch/x86/kernel/tsc.c | 6 ++++++
3 files changed, 31 insertions(+)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index bc27611..971f446 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -135,6 +135,7 @@ extern void init_apic_mappings(void);
void register_lapic_address(unsigned long address);
extern void setup_boot_APIC_clock(void);
extern void setup_secondary_APIC_clock(void);
+extern void lapic_update_tsc_freq(void);
extern int APIC_init_uniprocessor(void);

#ifdef CONFIG_X86_64
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 39517c0..c1ec995 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -570,6 +570,30 @@ static void setup_APIC_timer(void)
}

/*
+ * Install the updated TSC frequency from recalibration at the TSC
+ * deadline clockevent devices.
+ */
+static void __lapic_update_tsc_freq(void *info)
+{
+ struct clock_event_device *levt = this_cpu_ptr(&lapic_events);
+
+ if (!this_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
+ return;
+
+ clockevents_update_freq(levt, tsc_khz * (1000 / TSC_DIVISOR));
+}
+
+void lapic_update_tsc_freq(void)
+{
+ /*
+ * The clockevent device's ->mult and ->shift can both be
+ * changed. In order to avoid races, schedule the frequency
+ * update code on each CPU.
+ */
+ on_each_cpu(__lapic_update_tsc_freq, NULL, 0);
+}
+
+/*
* In this functions we calibrate APIC bus clocks to the external timer.
*
* We want to do the calibration only once since we want to have local timer
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 38ba6de..e0a6e20 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -22,6 +22,7 @@
#include <asm/nmi.h>
#include <asm/x86_init.h>
#include <asm/geode.h>
+#include <asm/apic.h>

unsigned int __read_mostly cpu_khz; /* TSC clocks / usec, not used here */
EXPORT_SYMBOL(cpu_khz);
@@ -1193,6 +1194,11 @@ static void tsc_refine_calibration_work(struct work_struct *work)
(unsigned long)tsc_khz / 1000,
(unsigned long)tsc_khz % 1000);

+#ifdef CONFIG_X86_LOCAL_APIC
+ /* Inform the TSC deadline clockevent devices about the recalibration */
+ lapic_update_tsc_freq();
+#endif
+
out:
if (boot_cpu_has(X86_FEATURE_ART))
art_related_clocksource = &clocksource_tsc;
--
2.9.0
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