Daniel,
On Thu, 27 Jun 2019, Daniel Drake wrote:
> Picking up this issue again after a break!
>
> We made some progress last time on reducing PIT usage in the TSC
> calibration code, but we still have the bigger issue to resolve:
> IO-APIC code panicing when the PIT isn't ticking.
Yeah. I was busy with other stuff and simply forgot.
> Being more conservative, how about something like this?
>
> + /*
> + * Record if the timer was in working state before we do any
> + * IO-APIC setup.
> + */
> + if (nr_legacy_irqs())
> + timer_was_working = timer_irq_works();
Nah. That extra timer works thing is just another bandaid.
What I had in mind is something like the below. That's on top of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/apic
Be warned. It's neither compiled nor tested, so keep a fire extinguisher
handy. If it explodes you own the pieces.
/me goes off to find icecream
Thanks,
tglx
8<-----------------
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -173,6 +173,7 @@ extern void lapic_assign_system_vectors(
extern void lapic_assign_legacy_vector(unsigned int isairq, bool replace);
extern void lapic_online(void);
extern void lapic_offline(void);
+extern bool apic_needs_pit(void);
#else /* !CONFIG_X86_LOCAL_APIC */
static inline void lapic_shutdown(void) { }
@@ -186,6 +187,7 @@ static inline void init_bsp_APIC(void) {
static inline void apic_intr_mode_init(void) { }
static inline void lapic_assign_system_vectors(void) { }
static inline void lapic_assign_legacy_vector(unsigned int i, bool r) { }
+static inline bool apic_needs_pit(void) { return true; }
#endif /* !CONFIG_X86_LOCAL_APIC */
#ifdef CONFIG_X86_X2APIC
--- a/arch/x86/include/asm/time.h
+++ b/arch/x86/include/asm/time.h
@@ -7,6 +7,7 @@
extern void hpet_time_init(void);
extern void time_init(void);
+extern bool pit_timer_init(void);
extern struct clock_event_device *global_clock_event;
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -820,6 +820,33 @@ static int __init lapic_init_clockevent(
return 0;
}
+bool __init apic_and_tsc_needs_pit(void)
+{
+ /*
+ * If the frequencies are not known, PIT is required for both TSC
+ * and apic timer calibration.
+ */
+ if (!tsc_khz || !cpu_khz)
+ return true;
+
+ /* Is there an APIC at all? */
+ if (!boot_cpu_has(X86_FEATURE_APIC))
+ return true;
+
+ /* Deadline timer is based on TSC so no further PIT action required */
+ if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
+ return false;
+
+ /* APIC timer disabled? */
+ if (disable_apic_timer)
+ return true;
+ /*
+ * The APIC timer frequency is known already, no PIT calibration
+ * required. If unknown, let the PIT be initialized.
+ */
+ return lapic_timer_period == 0;
+}
+
static int __init calibrate_APIC_clock(void)
{
struct clock_event_device *levt = this_cpu_ptr(&lapic_events);
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -58,6 +58,7 @@
#include <asm/acpi.h>
#include <asm/dma.h>
#include <asm/timer.h>
+#include <asm/time.h>
#include <asm/i8259.h>
#include <asm/setup.h>
#include <asm/irq_remapping.h>
@@ -2083,6 +2084,9 @@ static inline void __init check_timer(vo
unsigned long flags;
int no_pin1 = 0;
+ if (!global_clock_event)
+ return;
+
local_irq_save(flags);
/*
--- a/arch/x86/kernel/i8253.c
+++ b/arch/x86/kernel/i8253.c
@@ -8,6 +8,7 @@
#include <linux/timex.h>
#include <linux/i8253.h>
+#include <asm/apic.h>
#include <asm/hpet.h>
#include <asm/time.h>
#include <asm/smp.h>
@@ -18,10 +19,32 @@
*/
struct clock_event_device *global_clock_event;
-void __init setup_pit_timer(void)
+/*
+ * Modern chipsets can disable the PIT clock which makes it unusable. It
+ * would be possible to enable the clock but the registers are chipset
+ * specific and not discoverable. Avoid the whack a mole game.
+ *
+ * These platforms have discoverable TSC/CPU frequencies but this also
+ * requires to know the local APIC timer frequency as it normally is
+ * calibrated against the PIT interrupt.
+ */
+static bool __init use_pit(void)
{
+ if (!IS_ENABLED(CONFIG_X86_TSC) || !boot_cpu_has(X86_FEATURE_TSC))
+ return true;
+
+ /* This also returns true when APIC is disabled */
+ return apic_needs_pit();
+}
+
+bool __init pit_timer_init(void)
+{
+ if (!use_pit())
+ return false;
+
clockevent_i8253_init(true);
global_clock_event = &i8253_clockevent;
+ return true;
}
#ifndef CONFIG_X86_64
--- a/arch/x86/kernel/time.c
+++ b/arch/x86/kernel/time.c
@@ -82,8 +82,11 @@ static void __init setup_default_timer_i
/* Default timer init function */
void __init hpet_time_init(void)
{
- if (!hpet_enable())
- setup_pit_timer();
+ if (!hpet_enable()) {
+ if (!pit_timer_init())
+ return;
+ }
+
setup_default_timer_irq();
}
